ANNOUNCER: This is the Washington Week Webcast Extra.

GWEN IFILL: Hello, I'm Gwen Ifill.

Welcome to the Washington Week Webcast Extra.

I'm joined around the table by Doyle McManus of The Los Angeles Times and Reid Wilson of Morning Consult.

Candidates come, candidates go, and some stay for reasons that are hard to fathom.

This week, four candidates exited in the wake of poor showings in Iowa.

Did they leave an imprint behind?

Let's walk through each of them, starting with Rand Paul, who, Doyle, was on the cover of TIME magazine as the most interesting man to watch in 2016.

Except now it's watching his Senate race.

DOYLE MCMANUS: Exactly.

And one of the pundits, writing about Rand Paul, used the - said the coolest thing of all this week - said, you know, the problem with Rand Paul as the most interesting man in politics was that, by the end of this campaign, he was kind of boring.

GWEN IFILL: Well - DOYLE MCMANUS: I think that's unfair.

GWEN IFILL: I think it's unfair, but - DOYLE MCMANUS: I think Rand Paul was ambushed by events, because if you take yourself back two years, he was the libertarian candidate, he was the candidate of a minimal foreign policy.

He wanted to get out of foreign entanglements.

He even wanted to cut the defense budget, and he had some modest sympathy for Edward Snowden, the NSA leaker.

Boy, as soon as ISIS took over in Syria and part of Iraq did that set of ideas go out of fashion in the Republican Party.

GWEN IFILL: He missed his moment.

The moment missed him, it seems.

REID WILSON: Yeah.

I mean, he's not gone yet.

Doyle mentioned he's running for reelection for his Senate seat.

He's likely to win.

Kentucky's a very red state.

Some Republicans were a little nervous that he wasn't really paying attention to his Senate race.

Now, as he turns his attention back, he'll have a place in the Republican Party.

But this notion that there is a significant portion of the Republican Party ready to go down the sort of Ron Paul isolationist, libertarian lane, those voters weren't there this time around, whether it's because Rand couldn't duplicate sort of the excitement and magnetism of Ron, or just because ISIS became a threat and Donald Trump sucked the rest of the oxygen out of the room.

GWEN IFILL: Two other candidates who have done well in Iowa in previous years, basically by winning over the same groups of voters - Evangelicals and conservatives - Rick Santorum, Mike Huckabee.

Mike Huckabee's was my favorite exit ever, because he said the voters had just gotten sick of him.

But Rick Santorum was wearing that sweater vest till the last day.

What happened this time that was different from last time?

REID WILSON: Huckabee wasn't terribly wrong.

The longer somebody stays on the national stage these days, the more sick people get of them.

Look at the people who have excited the Democratic and Republican bases over the last - the last couple years.

Barack Obama, new guy on the scene; even beat John Edwards, who was the fresh face just four years before.

Now Ted Cruz is the hot new thing for Evangelical Christians.

Rick Santorum and Mike Huckabee are sort of old hat.

The shelf life for a national candidate these days is becoming shorter and shorter.

You don't hear people talking about their 20 years' experience in government or Washington, D.C. Just look at what's happening to, say, Jeb Bush versus Marco Rubio and Ted Cruz.

GWEN IFILL: Well, also, when you think about the candidates who are attractive to Evangelicals, Ben Carson was there, Ted Cruz was there, Marco Rubio speaks quite openly about Jesus Christ.

There was a lot of - there were a lot of choices.

DOYLE MCMANUS: And Donald Trump drew some of the Evangelical vote.

Not the - not the very conservatives, but the - GWEN IFILL: Not because - yeah, not for religious reasons, necessarily.

DOYLE MCMANUS: Not for religious reasons, for other reasons.

Boy, is this an illustration of the velocity of American politics, because people have forgotten that four years ago Rick Santorum came in second in the entire Republican race.

GWEN IFILL: He actually came in second - he came in first in Iowa, but no one knew it.

DOYLE MCMANUS: And he came in first in Iowa.

And one of the reasons Rick Santorum got into this race, I'm convinced, is it was kind of a grudge match, because he knew that if he had just won in Iowa the first time around, the first week around - GWEN IFILL: Maybe it would have changed everything.

DOYLE MCMANUS: - if he had put together - you know, in a funny way, Rick Santorum's economic philosophy was almost a precursor of some of the things Donald Trump has said, a kind of interesting economic populism.

Rick Santorum has spent four years looking back, saying, I could have been a contender.

GWEN IFILL: If only, if only, if only.

OK, on the Democratic side, Martin O'Malley, the third guy on the stage who was, I think, getting 1 percent of the vote, basically, if he was - on a good day, just melted away.

REID WILSON: And if you had put Martin O'Malley's resume - if you put all three of the candidates' resumes in front of the average Democratic voter with the names removed, you'd see a lot of them would have picked Martin O'Malley.

He did a lot on gay rights, on the minimum wage.

He checked basically every liberal box there was.

But he got immediately outmaneuvered to the left by Bernie Sanders.

His only hope was to run - was to become the main liberal alternative to Hillary Clinton, and there was a much bigger fish in that pond.

DOYLE MCMANUS: And Martin O'Malley's record as governor of Maryland, which he was running on - GWEN IFILL: A little baggage.

DOYLE MCMANUS: - basically evaporated, both because of the disturbances in Baltimore and because he couldn't even get his own - his own successor elected.

I did actually go the extra mile this week for you, Gwen, and talked to one of O'Malley's people, who said the verdict on the campaign in O'Malley world is at least he didn't hurt himself too much.

He might still be a possible vice president.

I think - GWEN IFILL: For whom, exactly?

DOYLE MCMANUS: I think secretary of commerce, maybe.

GWEN IFILL: (Laughs.)

OK. One more - two more people to watch.

Carly Fiorina, not out of the race, but she tried and failed to get on that debate stage.

Without being on a debate stage, is she going to make any kind of breakthrough?

Is there any way for her to do that?

REID WILSON: She had her moment in the sun when she got - she performed very well in the undercard debate.

She had at least one other good debate when she was back on the main stage.

But her poll numbers sort of tanked from there.

You know, she, like Ben Carson, like others, had their moment to rise and never really capitalized.

GWEN IFILL: And Jim Gilmore still in the race, got 12 whole votes in Iowa.

DOYLE MCMANUS: And he pointed out - best tweet of the week - that he is moving up because when this race started he was last in a field of 17, and now he's only the last in a field of I think it's nine.

GWEN IFILL: He can just sit at home and not drop out and continue to rise.

That makes the same amount of sense.

DOYLE MCMANUS: And it's cost him no money at all.

GWEN IFILL: No money at all.

Thank you.

(Laughter.)

While you're online, keep up with the race with the best reporters in the business, ours.

Every day we post their work in our News You Need To Know section.

That's at PBS.org/WashingtonWeek.

And we'll see you here next time on the Washington Week Webcast Extra.