Since the beginning of 2023, Republicans have spent nearly $78 million on advertising in New Hampshire, a sum that includes significant expenditures from candidates no longer in the race, such as Chris Christie and Tim Scott. As in Iowa, the top spender on TV in New Hampshire has been Stand for America, the Super PAC supporting Haley, which has run $23.5 million in advertising in the Granite State, according to AdImpact. No other candidate or group comes close to matching that number — the next-closest is Trump-supporting MAGA Inc., at $8.4 million. Haley herself has spent $5 million, while Trump has spent $7.4 million (candidates can buy ads on TV at a more favorable rate than outside groups).

You can see how big a priority New Hampshire has been for Haley and her allies, who began advertising in New Hampshire back in August. Just half of the pro-Haley spending in the state — $15.8 million of $31 million total between her campaign and supportive super PACs — has come within the last month of the race. Trump, meanwhile, is a relative newcomer to the airwaves. Of the $15.7 million in pro-Trump spending all cycle, almost all of it, $13.6 million, has come since Dec. 19, coinciding with Haley’s surge in the state’s polls.

A glance at TV spending also helps explain why DeSantis’s campaign floundered in New Hampshire, where the governor once polled as high as 25 percent but has fallen to less than 6 percent in the final 538 average before his exit from the race on Sunday. From an advertising perspective, DeSantis had effectively given up on the state in recent months. His Super PAC, the aptly named “Never Back Down,” spent $8 million in New Hampshire from April to November 2023, but hadn’t spent anything since.

—Jacob Rubashkin, Inside Elections

DeSantis was polling at only about 6 percent in New Hampshire when he dropped out of the race on Sunday, but 6 percent isn't nothing, and DeSantis's departure could help Trump on the margins tonight. According to an average of crosstabs from national primary polls, 48 percent of DeSantis supporters nationwide said that Trump was their second choice, while only 28 percent said Haley was. In New Hampshire, though, it was a little closer: 48 percent of DeSantis supporters there said Trump was their second choice, while 34 percent said Haley was.

If you take those numbers literally, we'd expect Trump to gain 3 points (48 percent of 6 percent) in New Hampshire from DeSantis's withdrawal, and Haley to gain 2 points (34 percent of 6 percent). However, DeSantis's endorsement of Trump on his way out of the race could mean Trump will gain even more ground. Overall, DeSantis's withdrawal is probably not good for Haley — although one New Hampshire poll, from Emerson College/WHDH-TV, did go against the grain and say that most DeSantis supporters would turn to Haley. These crosstabs all have very small sample sizes, and thus come with larger-than-usual margins of error, so we'll just have to see which of them is closest to the mark!

—Nathaniel Rakich, 538

In a January survey by Emerson College/WHDH-TV, just 52 percent of those who planned to vote in the New Hampshire Republican primary said they were registered as Republicans. Four percent said they were registered as Democrats, and 45 percent said they were registered as independents or with another party. (It’s worth noting that Democrats cannot vote in the Republican primary, so those 4 percent are going to be in for a disappointment when they show up to the polls.)

—Mary Radcliffe, 538

Although Iowa and New Hampshire both lead off the presidential nomination process and are both very white states, they have different-looking Republican electorates. Overall, New Hampshire GOP primary voters are less Republican, conservative and religious than Iowa Republican caucusgoers. This is due not only to differences across the two states' populations, but also divergent electoral rules that give New Hampshire a larger, less right-leaning electorate than Iowa. Thanks in part to these cleavages, the two states have voted for different winners in every open Republican presidential contest dating back to 1980.

One reason for these divergent results is that New Hampshire primary voters are less likely to identify as out-and-out Republicans than Iowa caucusgoers. Differing electoral rules help explain some of this contrast, as caucuses have lower participation rates than primaries. In Iowa, only registered members of a party may participate in that party's caucuses, and caucusgoers must attend these events at an appointed time on a weekday evening. By contrast, state-run primaries like New Hampshire's generally give voters roughly 12 hours to visit their regular polling place to cast a ballot, and they usually include at least a limited option to vote absentee. But critically, New Hampshire permits independent voters to participate in party primaries, unlike Iowa's caucuses and many other states' primaries.

New Hampshire Republican primary voters also tend to be less ideologically conservative than Iowa GOP caucusgoers. Once again, electoral rules play a role in this contrast. In part because of their higher barriers to participation, caucuses tend to attract the most committed and ideologically minded members of a party, whereas primaries attract a broader pool of voters, especially if independents are allowed to participate. Another reason for this ideological split is that New Hampshire's population has a smaller share of white evangelical Christians — a core part of the GOP base — than Iowa does. This is notable because white evangelical Christians are among the Americans most likely to identify as Republican, and they are more conservative than non-evangelical Republicans.

—Geoffrey Skelley, 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