One issue where Haley stands out is in foreign policy. Her history as Trump's ambassador to the United Nations gives her experience, and her policy positions place her at odds with the frontrunner. The Republican Party has followed Trump's lead in recent year's and become more isolationist. But Haley has taken a more traditional stance and has called for continuing aid to Ukraine, an issue that's becoming less popular with her party's voters. But she also has taken a hard line against China and supports continuing aid for Israel, which the Republican base also supports.

—Monica Potts, 538

Looking at towns where the vote is mostly counted, Trump is overperforming his 2016 benchmarks — but then again, he should be, since in 2016 he won with 35 percent of the vote in a many-candidate field. Trump will hope that the returns look like those in Farmington, where he's currently up 29 percentage points compared to his 2016 margin. But Haley will hope they look more like Newmarket or Conway, where Trump is only up by 15 or 16 percentage points.

— Dan Hopkins, 538 contributor

If voters in New Hampshire are thinking about the general election, Dan, that could be a problem for Trump. Last week, just 52 percent of Iowa caucusgoers voted for Trump. But according to a December YouGov/CBS News poll, likely New Hampshire GOP primary voters view the former president differently than those in Iowa. In that survey, 64 percent of likely voters in Iowa said that Trump would definitely beat Biden in November, while only 51 percent of New Hampshire voters said the same. Voters who said they were considering other candidates also had different reasons in the two states: 70 percent of likely New Hampshire voters who were considering voting against Trump said that one reason, of those provided to them, was that Trump is controversial, while only 57 percent of Iowans considering other candidates said the same. And more New Hampshirites were concerned about Trump's ability to beat Biden than Iowans considering other candidates.

—Mary Radcliffe, 538

Again per the Associated Press via The New York Times, Trump leads Haley 53 percent to 46 percent with 12 percent of the estimated vote counted. That's closer than the polls foresaw, but obviously not good enough for Haley so far.

—Nathaniel Rakich, 538

It's been only eight days since Iowa's first-in-the-nation caucuses last Monday, but a lot has happened since then. On the night of the caucuses, businessman Vivek Ramaswamy dropped out of the race and endorsed former President Donald Trump, and Florida Gov. Ron DeSantis followed suit on Sunday. With former Arkansas Gov. Asa Hutchinson also leaving the race last week, former U.N. Ambassador Nikki Haley is Trump's last major competitor standing.

And everyone has their eyes on New Hampshire as potentially the only state where Trump has a realistic chance of losing. Haley has invested heavily in New Hampshire and has been suggesting since early December that today's race would be the start of a competitive two-person primary between her and Trump. She's got her two-person race, but whether it will be remotely competitive remains to be seen. Trump has only continued to consolidate party support since his Iowa victory, and anything less than a convincing win for him would be surprising.

So when might we know? First polls will close tonight at 7 p.m. Eastern, and last polls will close at 8 p.m., which is the earliest time we could have a race projection. But as we did last week (when Trump's victory was projected only 30 minutes after caucuses had begun), we will of course be sticking around no matter what happens to see how each candidate does across the state and discuss what it could mean for the rest of 2024.

And that's not all! Granite State Democrats also have a primary today, and it's a weird one — New Hampshire is violating Democratic primary calendar rules by holding it so early. As a result, President Joe Biden isn't campaigning or even on the ballot, but his competitors, Rep. Dean Phillips and self-help author Marianne Williamson, are. While Biden isn't expected to face serious competition for the actual nomination, his margin of victory today as a write-in candidate could be one early sign of Democrats' grassroots enthusiasm for the incumbent.

Bookmark this page for updates and analysis throughout the night!

—Tia Yang, 538