If there's any state where Republican primary voters are likely to worry about Trump's ability to win in November, it might just be New Hampshire. In 2010, after the establishment-backed Kelly Ayotte won the GOP Senate primary there by a hair, she won the general election by more than 20 percentage points. In 2022, however, after the Trump-style Don Bolduc narrowly prevailed in the GOP Senate primary, he lost the general by almost 10 points.

—Dan Hopkins, 538 contributor

The Associated Press (via The New York Times) is showing 12 percent of the expected vote already counted on the Democratic side. Write-ins — likely mostly votes for Biden — lead with 73 percent, followed by Phillips at 22 percent and Williamson at 4 percent. That would be a robust showing for the president.

—Nathaniel Rakich, 538

At around 4:30 p.m., Americans for Prosperity Regional Director Greg Moore said on X (formerly Twitter) that he'd heard from sources in the New Hampshire secretary of state office that towns around the state had gone through more than 80 percent of GOP primary ballots available statewide, and that some towns were calling to ask for more to avoid running out. Polls in much of the state closed at 7 p.m Eastern, but a few places are open until 8 p.m.

Now, the Koch-affiliated AFP endorsed Haley to much fanfare earlier this cycle, so high turnout certainly would make Haley supporters feel hopeful about the number of independent voters taking part in the primary, who generally are more likely to support Haley than Trump. Still, ABC News's current total expected vote total in New Hampshire is 330,000 votes. Although that figure may change as the night wears on — it could go higher or lower — that many votes would represent nearly 30 percent of the state's entire voting-eligible population — that is, anyone who is eligible to register and vote. A turnout rate at that mark would be on par with the highest turnout in the state's modern history, which was the highly-competitive 2008 Democratic presidential primary.

—Geoffrey Skelley, 538

Four years ago, Democratic primary voters faced a situation similar to Republicans today: they were choosing a presidential nominee to unseat an incumbent with a low approval rating. But there's an important difference. Democrats emphasized electability, and though Biden was few Democrats' top pick — having finished fourth in Iowa and then fifth in New Hampshire — he benefited from the perception that he would run well against Trump.

For today's Republicans, the situation is much simpler: Trump is both the overwhelming first choice and the candidate they view as most electable. In a November 2023 survey that I conducted with the pollster YouGov, I found that 66 percent of Republican primary voters nationally backed Trump, but also that 72 percent of them thought that Trump was most likely to beat Biden. Despite some polling showing Haley running better against Biden nationally, most Republican primary voters see no trade-off between backing their preferred candidate (Trump) and winning in November.

—Dan Hopkins, 538 contributor

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