GWEN IFILL: It's finally here, caucus night in Iowa.

People will gather at sites all over the state to cast the first actual votes of the 2016 presidential election year. It comes after endless months of campaigning and more than $200 million spent on ads. The potential payoff? Forty-four delegates for Democrats, 30 for Republicans, and bragging rights.

Judy and the "NewsHour" team are on the ground in the Hawkeye State tonight — Judy.

JUDY WOODRUFF: So, Gwen, the candidates we're watching on this final day are also chasing another precious commodity, momentum. And so the focus in these final hours for them is on making sure anybody who is leaning or committed shows up when and where they're needed.

SEN. MARCO RUBIO (R-FL), Republican Presidential Candidate: Thank you so much. Thanks for all your help.

JUDY WOODRUFF: Most candidates were on the ground here in Iowa one last time today, making one last pitch to voters who may not have made up their minds, and urging those already on their side to turn out tonight.

On the Democratic side, Bernie Sanders is facing the question, will his supporters, many of them first-timers to the caucuses, show up? He revved up volunteers in Des Moines today.

SEN. BERNIE SANDERS (VT-I), Democratic Presidential Candidate: So what is our job today? It's to make sure we have the highest voter turnout possible. That happens, we win. Let's go get them. Thank you all.

JUDY WOODRUFF: Hillary Clinton was also in Des Moines. With pastries in hand, she cheered her volunteers through their last-minute push.

HILLARY CLINTON (D), Democratic Presidential Candidate: Thank you. We will do it together.

JUDY WOODRUFF: In late polls, Clinton has a small advantage. But with Sanders well ahead in next week's New Hampshire primary, Clinton's feeling the pressure here.

HILLARY CLINTON: Come caucus for me tonight. OK?

JUDY WOODRUFF: On the Republican side, Donald Trump is also relying on first-time caucus-goers for support. He made his plea today in Waterloo in Northeastern Iowa.

DONALD TRUMP (R), Republican Presidential Candidate: We are leading all the polls and we're leading in Iowa, but it doesn't mean anything. You have got to go out tonight and caucus. Hopefully, tonight, we're going to have the beginning of what is going to be in a certain way a very positive revolution.

JUDY WOODRUFF: Trump has opened up a lead in recent polls on his closest rival, Ted Cruz. But the Texas senator is hoping his campaign's organization and outreach to evangelicals will work in his favor.

SEN. TED CRUZ (R-TX), Republican Presidential Candidate: We have now been to all 99 counties in the great state of Iowa. This is our final stop on caucus day.

JUDY WOODRUFF: Marco Rubio, who's polling third here, has been tamping down expectations, even as he works overtime.

SEN. MARCO RUBIO: We recognize we're not the front-runner. We know we are an underdog, but we feel good about it.

JUDY WOODRUFF: The candidates who've struggled in Iowa aren't even sticking around for the caucuses.

GOV. JOHN KASICH (R-OH), Republican Presidential Candidate: If I do well in New Hampshire, everybody's going to know who I am.

JUDY WOODRUFF: John Kasich, staking his campaign on the New Hampshire primary, was there through the weekend.

And while Jeb Bush and Chris Christie were here earlier today, both will be following caucus results from the Granite State.

There is one more wild card: the weather. Much of Iowa is in for a winter storm in the hours just ahead. Whatever tonight's results, the presidential race is heading into new turbulence all its own.

GWEN IFILL: Hi there, Judy.

You and I combined have covered our share of Iowa caucus nights, but this one seems more mysterious, more kind of amazing and unpredictable than ever.

JUDY WOODRUFF: You're right.

You and I both covered these Iowa caucuses before. And I can remember some really unpredictable ones in the past, but, Gwen, nothing like this.

When we're on the Republican side, you have a man who never served in public office before running for the highest office in the land, and he's been leading in the polls ever since he first got into the race. That's Donald Trump. The question tonight, of course, as everybody has been saying, is, can he translate that enthusiasm into getting people to show up to their local schoolhouse, their church, or wherever these caucuses take place and get them to stand there and stand up and say, I'm for Donald Trump?

On the Democratic side, just as unpredictable, Hillary Clinton, the favorite, and yet Bernie Sanders, the one Democratic socialist in the U.S. Senate, is giving her a run for the money. And the question is the same there. Can he turn that enthusiasm into votes?

GWEN IFILL: It seems like all the conventional wisdom is out the window tonight.

JUDY WOODRUFF: Well, it really is.

And, you know, I just heard the most revered pollster in the state say, Ann Selzer, says that she — when people say what are the issues in this campaign, she said there really haven't been issues, especially on the Republican side. She said, this is an election about mood and about who can take the country to the next level, to the future.

And so she compared it — she said, this is an election that stands alone. And I think we will see tonight if that turns out to be the case.

GWEN IFILL: Good to see you on the campus of Drake University in Des Moines tonight. Thanks, Judy.

Judy will be back with a closer look at the key voters who could determine tonight's outcome after the news summary.