GWEN IFILL: Hillary Clinton's email contrition, Donald Trump's effort to be taken seriously, and the Iran deal inches closer to approval - the policy and the politics, tonight on Washington Week.

SECRETARY OF STATE JOHN KERRY: (From video.)

Sanctions alone were not getting the job done.

They were failing to slow, let alone halt, Iran's relentless march towards a nuclear weapons capability.

GWEN IFILL: The White House rounds up the votes they need to stop Congress from killing the Iran nuclear deal.

SENATOR ROBERT CASEY (D-PA): (From video.)

We're the only country in the world that has the military capability to take out Iran's program today, tomorrow and into the future.

GWEN IFILL: But is the fight over?

WISCONSIN GOVERNOR SCOTT WALKER (R): (From video.)

I'm frustrated that there's not enough votes to block it today, but as president I will terminate that bad deal on day one.

GWEN IFILL: As the 2016 campaign steams toward Labor Day, more shoes drop.

Donald Trump pledges to stay a Republican.

DONALD TRUMP: (From video.)

So I will be totally pledging my allegiance to the Republican Party and the conservative principles for which it stands.

GWEN IFILL: And he takes fresh aim at Jeb Bush.

FORMER FLORIDA GOVERNOR JEB BUSH (R): (From video.)

Yes, they broke the law, but it's not a felony.

GWEN IFILL: And Bush aims right back.

JEB BUSH: (From video.)

This is not a guy who's a conservative.

And using his own words is not a mischaracterization.

They came out of his own mouth.

GWEN IFILL: Carly Fiorina likely makes the cut for the next GOP debate.

CARLY FIORINA: (From video.)

I think Donald Trump and Jeb Bush are going at it as frontrunners are going to do in a presidential campaign.

GWEN IFILL: And Joe Biden's in the speculative spotlight.

VICE PRESIDENT JOSEPH BIDEN: (From video.)

The most relevant factor in my decision is whether my family and I have the emotional energy to run.

GWEN IFILL: The hits keep on coming.

Covering the week, Peter Baker, chief White House correspondent for The New York Times; Jeanne Cummings, political editor for The Wall Street Journal; and Karen Tumulty, national political correspondent for The Washington Post.

ANNOUNCER: Award-winning reporting and analysis.

Covering history as it happens.

From our nation's capital, this is Washington Week with Gwen Ifill.

Once again, from Washington, moderator Gwen Ifill.

GWEN IFILL: Good evening.

Today, Hillary Clinton demonstrated just how seriously she's taking the questions that have dogged her campaign since it emerged that she exclusively used a private email server during her time as secretary of State.

Sitting down with NBC's Andrea Mitchell, she conceded that her shifting explanations over time may have damaged her credibility.

FORMER SECRETARY OF STATE HILLARY CLINTON: (From video.)

At the end of the day, I am sorry that this has been confusing to people and has raised a lot of questions.

But there are answers to all these questions, and I take responsibility, and it wasn't the best choice.

GWEN IFILL: Secretary Clinton also tested out the message she plans to use to turn that corner.

HILLARY CLINTON: (From video.)

I want to be the president who deals with all those big problems that are in the headlines, but also those problems that keep families up at night.

GWEN IFILL: So first, Karen, what did we learn new, if anything, about the whole email controversy?

KAREN TUMULTY: You know, not really much of anything.

You know, incremental stuff that it - you know, that it was her lawyers that had gone through her emails and decided which were personal and then which were going to be turned over to the State Department.

She gave a little bit about the process by which she decided to destroy all of her personal emails.

But I think the - I think the message, which is one that she began giving a week ago - she's really pivoted from, you know, this is nothing and being sort of dismissive about it to trying to convey that she understands that people are concerned about this.

GWEN IFILL: This new - as we know, on a monthly basis we're getting a new tranche of emails that have been released from her server, and the ones this week seem to be kind of, I don't know, more told us about her personality and the way she communicates and the way she gets advice than anything else.

JEANNE CUMMINGS: Well, that is one of the few things you can glean from so many emails coming at you at once and many of them being blacked out.

GWEN IFILL: Seven thousand.

JEANNE CUMMINGS: But, you know, she talked - you can see that she would interact on a very familiar level in terms of watching television shows about politics.

Definitely a lot of politics in those emails in that Mark Penn was sending her updates.

This was during the 2010 period, this last batch.

So she got updates from Mark Penn, Sidney Blumenthal.

We found it interesting that Sidney Blumenthal, she tried to hire him; the White House blocked her - GWEN IFILL: Remind people who that is.

JEANNE CUMMINGS: He is a longtime Clinton aide.

He was in President Bill Clinton's administration.

But the White House blocked his hiring for the State Department, and yet, when you look at the emails, he certainly sought to have a very big role in terms of giving her guidance.

And so you do glean a few things like that out of these.

But this group, as you said, was expected to be nonconsequential because the things that might be particularly dicey they're fighting over now.

The State Department and the intelligence agencies are fighting over what should be classified and what shouldn't be.

GWEN IFILL: One of the things that's interesting about this period in the campaign is that Hillary Clinton - this is maybe only the second or third time she's sat down and had a serious, extended interview since she's actually been in the race, and this is as apologetic or accessible-seeming that she has striven to be since then.

Does that represent their internal polling or some just - or the external polling that we're all looking at, that shows that people are beginning to ask questions about her trustworthiness?

KAREN TUMULTY: You know, certainly they're seeing what everyone else is seeing in the polls.

It's not that she doesn't maintain an absolutely commanding lead over any of her potential rivals in national numbers, but we are seeing Bernie Sanders is creeping up on her in Iowa.

Some polls have him ahead in New Hampshire.

The real erosion in her numbers has been in how people regard her - whether they consider her trustworthy, whether they approve of her.

And these are unforced errors.

You know, the campaign also realizes that, you know, they missed some opportunities back when The New York Times first revealed that this private email system existed to have been more forthcoming then, and perhaps she would not be having these problems now.

JEANNE CUMMINGS: I think also it is the campaign.

I mean, her donors - many of her donors have been shaken by not just what happened, but the handling of the political fallout from it all.

We know that they are - they are inviting donors individually up to Brooklyn to sit down with Robby Mook, talk these things through.

GWEN IFILL: Her campaign manager.

JEANNE CUMMINGS: A lot of care and feeding of these donors.

So it isn't just the polls; it's also her supporters have been rattled by their handling of all of this.

PETER BAKER: Well, and that leads us right to Joe Biden, right?

Why would he be considering jumping into the race at this late date?

He has no fundraising organization.

He has no campaign operative to speak of.

And yet there's a lot of interest.

Why is there a lot of interest?

GWEN IFILL: You know, before that I'm going to - I'm going to actually ask us to roll a little bit of Joe Biden last night.

We saw him go to speak.

He was speaking - appealing to Jewish groups about the Iran deal and there was a Q&A, and he was asked about whether, in fact, he was going to run.

And his answer was pretty sober.

Let's listen.

VICE PRESIDENT JOSEPH BIDEN: (From video.)

Everybody talks about a lot of other factors - the other people in the race and whether I can raise the money and whether I can put together an organization.

That's not the factor.

The factor is, can I do it?

Can my family undertake what is an arduous commitment that we'd be proud to undertake under ordinary circumstances?

But the honest-to-God answer is I just don't know.

GWEN IFILL: I've covered politics for a long time.

I have never heard someone considering running for president sound so mournful.

He goes on to talk about the loss of his wife and daughter all those years ago.

That does not sound like someone who's got the fire in the belly.

KAREN TUMULTY: It also does not sound like Joe Biden, the Joe Biden that we have seen over decades.

But there are people out there who would really like to see him run, and a number of them - speaking of the donor community - a number of them are people who gave money to Barack Obama in the 2008 primary race and have been sitting on the sidelines and not showing up for Hillary Clinton.

JEANNE CUMMINGS: But I do think that - I think Biden, based on our reporting - what is happening to Hillary is really not influencing where the vice president finally ends up on this.

Ultimately, I think the vice president has made it clear to his friends and supporters he thinks he'd be the better president.

So it doesn't really matter if Hillary's at 50 or 68 (percent) or whatever, he thinks - GWEN IFILL: A lot of people think they would be the better president, but can they get elected to be president?

JEANNE CUMMINGS: Well, and he does think he can raise some money and find a path.

It's really all about himself.

It really is about himself.

And I don't believe we're going to - he said a decision will come in late September.

I think he's further away from it than that.

I think it'll even be later than that because he's nowhere near the point of a man ready to walk out on the campaign trail.

PETER BAKER: Think of where he's at, right?

He is at a stage in his career where this is it.

This is the last decision he's going to make when it comes to a political career.

If he runs, then there's a future ahead - probably a very difficult path if he has any chance of beating Hillary Clinton, but at least a future.

Otherwise, if he makes a decision I'm not going to run, that's pretty much it.

And having just gone through this terrible trauma of his son dying prematurely, he's clearly wrestling with, you know, his own, you know, mortality, his own political future, his own rest of his life.

He's got 18 months left in office.

GWEN IFILL: There's something quite remarkable watching someone wrestle with that in public.

PETER BAKER: In such a public way.

GWEN IFILL: Let's talk about the Republican side of this equation, because the Republican frontrunner appears to have settled on a single message.

Whether he is asked about Iran or the economy or immigration or the Quds Force in Iraq, Donald Trump's answer is essentially the same: he is great, and our heads will spin when he is president - a Republican president.

DONALD TRUMP: (From video.)

I will be totally pledging my allegiance to the Republican Party and the conservative principles for which it stands.

I see no circumstances under which I would tear up that pledge.

GWEN IFILL: The pledge in question is a nonbinding promise that Trump will not run as an independent in 2016.

Now, remind us why that was even an issue, Jeanne?

JEANNE CUMMINGS: Well, at the first debate there was all kinds of rumors in the air that he might run if he - if he didn't come out of the nomination, run as an independent and kill the party.

So Fox asked him - or asked all of them, you know, who will not pledge to support the Republican nominee, and he did indeed raise his hand.

And at that point, it sent shockwaves through the party and has been an obsession ever since, the worry that he would actually do this.

So for him to put it to rest is, for the Republicans, a pretty - a big relief.

GWEN IFILL: Did he put it to rest, though, Karen?

He's - you know, this isn't a legally binding document.

KAREN TUMULTY: It's not a legally binding document, and it is provisional on him continuing to believe that the Republican Party is treating him fairly.

He said that a number of times.

GWEN IFILL: Many times.

What does that mean?

I kept - I keep wanting to shout at the TV screen: What is fairly?

How do you define that?

KAREN TUMULTY: I think just watch his Twitter feed and you will get moment by moment who he thinks is treating him fairly or not.

(Laughter.)

So this is good news and bad news for the Republicans.

I mean, this - the good news is that they are now - that Donald Trump is solidly aligned with the Republican Party.

The bad news is that the Republican Party is now solidly aligned with Donald Trump.

So this, again, could - you know, as much as they want to talk about him like he's some sort of force of nature out there who, you know, when he says something to alienate Hispanics or whatever that he's not speaking for the party, it's I think a little bit more difficult to do that now.

GWEN IFILL: It is interesting to watch the other candidates wrestle with what to do, and the person most interesting to watch this week was Jeb Bush.

And there was even a dispute that sprung up between the two of them where they talked about what language you're allowed to speak on the campaign trail.

Let's listen to that exchange.

JEB BUSH: (From video.)

Here I am, a candidate for president of the United States, believing that we should campaign "con brazos abiertos," with our arms wide open.

DONALD TRUMP: (From video.)

When you get right down to it, we're a nation that speaks English.

And I think while we're in this nation we should be speaking English.

GWEN IFILL: Now, the interesting thing - (chuckles) - because there are so many interesting things - but Jeb Bush speaks incredibly fluent Spanish.

His wife is a native Spanish speaker.

So what is this really about?

Is this about some larger issue?

JEANNE CUMMINGS: Absolutely.

These two - the biggest change this week came from the Bush camp.

Trump has been steadily pummeling Jeb Bush.

The Bush campaign had to decide, really, what were they going to do.

And their analysis was, if we - if we keep staying where we and kind of trying to make fun of it and really not responding, we look weak, which only reinforces Trump's attack.

So the option - the other option was go on the attack and risk whatever wrath is coming at them after that.

KAREN TUMULTY: And Jeb Bush, of course, being the one who said he wasn't going to run unless he could do it joyfully.

There is, in fact, one joyful candidate out there, and that is not Jeb Bush.

(Laughter.)

PETER BAKER: No joy in Mudville right now.

(Laughter.)

KAREN TUMULTY: That's right.

(Laughs.)

GWEN IFILL: Well, so then what do any of the other candidates do about it?

We see Ted Cruz's response, which is come, join me, let's protest arm-in-arm together.

We see Scott Walker's kind of searching for a place to land and not really attacking him.

We see Carly Fiorina saying - much more mildly, I think - but criticizing him for not being ready to be president.

JEANNE CUMMINGS: She had the best criticism of him in that first debate, and that's one of the things that set her apart.

She was the one who said, did you get your phone call from Bill Clinton to talk about your presidency?

I didn't get one, and of course Donald Trump did indeed talk with Bill Clinton about his presidential campaign.

So, in fact, she has had the meanest and sharpest attack on Trump; she just hasn't said it lately.

GWEN IFILL: So it's kind of significant that she's going to - that she made the cut, apparently, this week for the next debate we're going to see in a couple of weeks that CNN is sponsoring.

JEANNE CUMMINGS: And Christie is promising to be more aggressive, and he has - he's been one willing to criticize Trump.

The one who has stayed under the radar is Marco Rubio.

He has not said anything much at all about Trump, and as a consequence Trump has not set his aim on him either.

GWEN IFILL: Let's talk about Carly Fiorina for a minute because you're right, she was in the - at the kiddies' table in the first debate.

They've changed the rules at CNN, so she is allowed to participate in the major debate.

Does that make a difference about the - what the chemistry will be up there on that stage?

KAREN TUMULTY: Well, and by the way, they changed the rules in a way that I think most people think made the rules more fair because instead of using old polls they're using more recent polls.

One thing, there may be 11 candidates on the stage now instead of 10.

There will be a woman on the stage where there wasn't one before.

But I do think that Carly Fiorina had earned her way onto that stage by really demonstrating that she, outside of Donald Trump, probably has the best sort of thrust-and-parry kind of skills of any of the other candidates.

And you know, you talk to people in Silicon Valley and they say that was what she was known for, too, when she was the head of HP, that she could do a sales presentation, a marketing presentation like nobody they had ever seen before.

GWEN IFILL: Peter, let me ask you a question, actually, because I am - one of the things that happened in the last 24 hours is Donald Trump gave an interview to Hugh Hewitt, the conservative radio host, in which, among other things, Hugh Hewitt asked him about a couple of, I don't know, foreign names, people who are enemies to America, and whether he knew who they were.

And Trump's response, as is typical now, was to push back pretty aggressively and say that was a gotcha question.

Is that something, however, that Americans expect of their candidates, to know the answers to questions like this?

PETER BAKER: Yeah, I mean, it's a good question.

Remember, in 2000, when George W. Bush was running, he got asked the names of four foreign leaders and he only got one, one-and-a-half, depending on how you grade him.

It didn't hurt him, but it obviously did make the point that he wasn't schooled in foreign policy.

That didn't matter so much in 2000.

It was a pretty peaceful time and we were focused mostly on domestic issues.

This is a different moment.

I mean, we have big issues in the Middle East right now.

The difference between the Quds Force, which is the paramilitary organization of Iran, which has been fighting us and our allies for a lot of years, and the Kurds, who are our friends and have been fighting on our side against ISIS, it's a pretty big difference.

And so whether the average voter connects to that or not I don't know.

I mean, that's - probably not.

They probably don't focus that deeply on it either.

But it does - it's more relevant, probably, to today's issues than it has been in the past.

KAREN TUMULTY: And Hugh Hewitt put those exact same questions to Carly Fiorina and she actually was - GWEN IFILL: And to other candidates as well.

KAREN TUMULTY: And she was able to answer them.

And again, it shows, I think, the level of preparation that she's probably going to bring to the debate as well.

PETER BAKER: And even if - and even if you don't know who they are, his dismissive tone about, well, it doesn't matter because they won't be in office when I get into office anyway, they'll probably be gone and I'll just be dealing with the next ones - I'll know who they are better than I know who you are, he said to Hugh Hewitt.

GWEN IFILL: Well, let's stay with foreign policy for a moment because the numbers have been adding up in Washington.

Enough senators now, and House members also, signed up this week to guarantee Congress will not be able to turn back the Iran nuclear deal.

But until the final votes actually occur, the debate rages on.

Secretary of State Kerry said the White House is still pushing for 41 senators to block a vote of disapproval.

SECRETARY OF STATE JOHN KERRY: (From video.)

We want anybody and everybody, hopefully, to be able to vote for it.

We're going to continue to try to persuade people up until the last moment.

And our hope is that that number will grow, obviously.

But it is - it is enough to sustain the president's veto, but that's not satisfactory for us.

GWEN IFILL: Now, opponents aren't done yet.

Ted Cruz, as we mentioned, has asked Donald Trump to rally against the deal at the Capitol next week, and more than one candidate has pledged to take it apart.

SENATOR MARCO RUBIO (R-FL): (From video.)

If I'm president, that deal won't survive.

It's not a treaty.

It's not legally binding on the United States.

It's a decision the president's made to use the national security waiver of an existing sanctions law not to impose sanctions on Iran.

GWEN IFILL: So, Peter, who has the upper hand tonight?

PETER BAKER: Well, I mean, it was a - you know, a good week for the president in the sense that he now knows that the deal can go forward for the rest of his administration.

Having said that, it's lowering the bar of what we consider to be a victory that you can get a third of each house to simply back you.

This is not an approval of his deal, this is simply avoiding defeat.

And it doesn't send a great message, perhaps, to the international community, but on the other hand, it allows him to move forward.

He brought the king of Saudi Arabia to the White House today.

They were not very happy with this deal, but they've basically come to grudgingly accept it.

So he's trying to move on, both internationally as well as at home.

You know, can the next president - can a Republican president undo this deal on day one?

I don't think it's that simple because it's not a simple thing as the United States having a deal with Iran.

It's six world powers, for one thing.

The U.N. Security Council's going to be voting on this.

It's going to put procedures in place.

The Europeans are not going to simply put sanctions back just because an American president decides he doesn't like this deal.

The whole thing becomes a much more confused mess if that happens.

GWEN IFILL: But I seem to recall that one of the great weaknesses of the health care law and the - political weaknesses of the health care law - was that it was perceived that it was agreed to without any Republican support.

PETER BAKER: Right.

GWEN IFILL: And in the end, a victory, as this has now been - or lack of defeat here may not require any Republican support.

PETER BAKER: No, it's simply his own party.

He's simply talking to Democrats at this point.

He's got no hope of getting any Republican votes in either house, it looks like, at this point, and he's simply trying to get most of his Democrats to stand by him.

Senator Ben Cardin of Maryland - a low-key, soft-spoken Democrat - today said he can't vote for the deal.

He's the third Democratic senator to say so.

And - GWEN IFILL: And the head of the Foreign Relations, or - PETER BAKER: And the head of the - yeah.

And so, you know, he's simply trying to keep his own people together.

That's kind of a minimalist requirement.

It's not the same thing as building a national consensus behind the deal.

He's hoping, I think, that if - 18 months later, when he leaves office, it will seem like a better deal, perhaps, than it does today.

JEANNE CUMMINGS: Peter, though, when they started out it seemed like their whole strategy was just to make sure the House was, you know, their firewall, that the House would help uphold his veto.

So it seems to me getting - they may get enough Democratic senators to block the vote itself if they get to 41.

And that's going, basically, from zero to 41, or some small number to 41.

As I read it, I didn't think they ever thought they'd do this well in the Senate.

PETER BAKER: Well, that's a good point because there are a number of senators who had teamed up with Republicans early on to say we think this whole Iran negotiation is flawed and possibly dangerous.

And a lot of those critics in the Democratic Senate caucus have kind of come around - again, grudgingly.

They're saying, look, I don't necessarily think this is a great deal, but the alternative isn't any better.

There is no other alternative at this point.

JEANNE CUMMINGS: How did the White House get them to do that, or?

PETER BAKER: Well, partly they've been much more aggressive in trying to lobby and to put information in front of their friends than they often have been.

This has not necessarily been a White House with a great reputation for working with Congress, even its own party.

This time around I think they've been much more assertive about getting out in front of a cause.

In fact, I've heard from Democrats who say they've heard from the White House more on this issue than any issue in six years - in the six-and-a-half years he's been there.

KAREN TUMULTY: And was there actually a backlash to Bibi Netanyahu's decision to come and speak before the Congress?

PETER BAKER: I think there was, and I think that the Republican opposition in some ways gets up the backs of the Democrats so it becomes more of a partisan thing.

And instead of bringing Democrats along with them, Republicans kind of lost their chance with some of them to form a bipartisan consensus against the deal.

And I think, you know, on some level a certain reality kind of sets in where there isn't another choice.

It's not like you can say let's go back to the bargaining table because the other world powers aren't willing to go back to the bargaining table.

And so they - he's basically said to his fellow Democrats, this is it now.

You know, it's not like you can say I want a better deal; you have to take this deal or no deal.

GWEN IFILL: We probably can - you noticed when we were playing that clip earlier of Joe Biden he was wearing a yarmulke.

He was speaking to - was sent to Florida to kind of persuade Jewish supporters that this is a good deal.

And he has been a not-so-secret weapon in trying to defuse some of the real strong pushback among friends of Israel about - who are worried about this deal.

PETER BAKER: Right.

And the president himself expressed - during his time in Alaska I think he gave - he said he resented that he was being called an anti-Semite; that simply because he was proposing a deal that was not accepted by the current Israeli government did not mean that he doesn't have Israel's back.

And part of his persuasion campaign with the Democrats was to send out a letter that said here are all the different ways I'm going to try to help Israel defend itself and make sure its security is beefed up and so forth.

So he's tried to make clear that being for this deal does not have to mean you're against Israel.

GWEN IFILL: OK. Well, we'll be watching this as this moves on because, once again, it doesn't end here.

Thank you very much, everybody.

We have to go for now, but as always the conversation will continue online on the Washington Week Webcast Extra, where among other things we'll talk about the president's historic trip this week to the Alaskan Arctic.

Keep up with developments with Judy Woodruff and me on the PBS NewsHour.

And we'll see you here next week on Washington Week.

Have a restful Labor Day.

Good night.