AMNA NAWAZ: Welcome to the "News Hour."

It was a dramatic beginning to the 119th Congress, as Republicans prepare for unified control in Washington.

And for the House GOP, unified it was, albeit with some delay.

Despite a handful of initial holdouts, Representative Mike Johnson of Louisiana was reelected speaker of the House on the first ballot, earning support from all but one member of his party.

Johnson spoke about his priorities for the coming year.

REP. MIKE JOHNSON (R-LA): After four years of high inflation, we have a big agenda.

We have a lot to do, and we can do it in a bipartisan fashion.

We can fight high inflation, and we must.

We'll give relief to Americans, and we'll extend the Trump tax cuts.

AMNA NAWAZ: Speaker Johnson will now have to wrangle the narrow Republican majority to implement president-elect Donald Trump's agenda.

Lisa Desjardins has been tracking the maneuvering on Capitol Hill all day, and she joins me now.

So, Lisa, a dramatic day indeed.

Walk us through how this vote unfolded.

LISA DESJARDINS: Maneuvering is the right word, Amna.

Walking into the House today, it seemed the odds were against Mike Johnson winning on the first vote, or even today at all.

He had 12, at least, members that I knew of who had serious doubts and were ready to vote no.

And, in fact, he was losing this race for at least an hour.

Let's go over those numbers.

To become speaker of the House, Johnson needed 218 votes, and, initially, he received only 216.

Three Republicans voted against him, voted for someone else.

And those members were members of the hard right.

All three of them, Thomas Massie of Kentucky, Ralph Norman of South Carolina, Keith Self of Oklahoma, prominent fiscal hawks, they care about the debt and deficit.

They think that Johnson botched the last funding deal, and they are someone who they believe that he has not been a strong enough speaker.

But over the course of an hour, they kept that vote open.

And thanks to phone calls with former President Donald Trump, two of those members switched their vote, and Johnson was able to become speaker on the first vote.

AMNA NAWAZ: So tell us more about why they changed their minds.

Was it just those calls, as you mentioned, from president-elect Donald Trump, and what does this mean for what comes ahead?

LISA DESJARDINS: You know there's almost never a universal agreement about anything at the Capitol, but there is universal agreement tonight that Mike Johnson is speaker because of former President Donald Trump.

And you could see, even on the House floor, he's someone whose endorsement earlier this week was pinging around, but it was not enough to get a dozen members over the finish line for Johnson.

Instead, we saw a member, Marjorie Taylor Greene, on the phone, on the chamber floor, trying to help negotiate and spread word, get the Trump message out.

And, indeed, the members who talked to Trump said that it was in conversations with him, those two members who changed, that they decided to reverse course.

REP. KEITH SELF (R-TX): We had a lively conversation, and I was very honest with the president, which I think everyone ought to be, that I thought that we needed a stronger negotiating position.

I think we need a very strong Republican Conference, and I wanted some changes.

LISA DESJARDINS: Now, those members told us, one of them told me that they left with the understanding, and been reported elsewhere, that Speaker Johnson would put more hard right members on negotiation teams, but they said, there wasn't any direct promise.

There's been talk of making one member a chairman.

They said nothing like that.

Now, it's just the easy part, I have to say, and to some degree, but, at the same time, Democrats told me they were not surprised that Johnson was in a pickle.

They were surprised he won the first vote, but not surprised that things began with a roller coaster.

Let's listen.

REP. JARED MOSKOWITZ (D-FL): It just seems that the 119th Congress is going to pick up right where the 118th Congress left off.

And what I'd say to my colleagues across the aisle is Democrats like myself are ready to work with them where we can.

LISA DESJARDINS: This is the easy part, as I say, two Republican members expected to join Trump's administration and then the margin will just get narrower, Amna.

AMNA NAWAZ: So the easier part is behind him now.

Mr. Johnson managed to capture the gavel on that first ballot, but how secure is his speakership?

LISA DESJARDINS: It still could be in danger, depending on how things go.

But, tonight, just in the last hour, the House passed a new rules package that actually will make it tougher for Republicans to oust him.

It will now require nine members, instead of one.

Also, they're getting rid of the Office of Diversity and Inclusion.

And, tonight, we had the House Freedom Caucus members send out a letter essentially warning Johnson that if he doesn't meet their demands going forward, they still will be on top of them and that they could use this new harder-to-use method to oust him.

I also want to mention today was the first day in the Senate.

Worth noting the Republicans there with 53 seats, it's the largest majority for either party in a decade, John Thune now the Republican Senate leader.

Amna, he is the first Republican leader in the Senate since 2007, the first new one, when Mitch McConnell took office.

2007, Amna, that was the year the iPhone was invented, so a generational change happening today in the U.S. Senate.

AMNA NAWAZ: Generational change and a big day on Capitol Hill.

Lisa Desjardins is covering it all.

Lisa, thank you.

LISA DESJARDINS: You're welcome.