Despite being Haley's home state, South Carolina is demographically much friendlier turf for Trump than Haley. Exit polls dating back to the 2012 Republican nomination race suggest that South Carolina's electorate will likely be more heavily Republican, more conservative and more religious than New Hampshire's.

In recent GOP primaries, at least 7 in 10 South Carolina voters identified as Republican and about a quarter called themselves independent. By contrast, only around half of New Hampshire's GOP primary voters called themselves Republicans, while more than 40 percent said they were independent. This should help Trump, who performs best among self-described Republicans. In New Hampshire last month, the exit poll found Trump attracted 74 percent of the vote among Republicans while Haley won 58 percent of independents. Recent South Carolina polls have found similar splits, with Trump surpassing 70 percent among Republicans and Haley narrowly ahead among independents.

Beyond party identification, Trump also stands to benefit from South Carolina's larger share of conservative-minded voters. More than 35 percent identified as "very conservative" in South Carolina's 2012 and 2016 GOP primaries, whereas New Hampshire's primary electorate didn't surpass 26 percent in that category in 2012, 2016 or 2024. And Trump does best among the most conservative voters in the polls: For instance, a Monmouth University/Washington Post poll of South Carolina in late January found Trump garnering 80 percent support among very conservative voters, compared with 59 percent among somewhat conservative voters and just 33 percent among moderate or liberal voters.

Trump's greater appeal among conservatives is connected to his increased support among white evangelical Christian voters. Voters who fall in that category tend to identify as more conservative than non-evangelicals, and they will likely make up a majority of South Carolina's GOP primary electorate. In 2012 and 2016, about two-thirds of GOP primary voters there identified as white born-again Christians, whereas less than a quarter said the same in New Hampshire. The late January Monmouth University/Washington Post poll found Trump attracting support from 69 percent of white evangelicals, compared with 46 percent of other voters.

—Geoffrey Skelley, 538

Haley may have come up through South Carolina politics, but her old colleagues are mostly supporting Trump. Both of the state's senators, its governor, its lieutenant governor, its attorney general, its secretary of state, its treasurer, its agriculture commissioner and five of its six Republican U.S. representatives have endorsed Trump. In fact, many of them announced their endorsement quite early in the campaign, when Trump visited South Carolina in January 2023 — a coordinated show of early strength in a rival's home state. By contrast, Rep. Ralph Norman is the only major South Carolina politician who is supporting Haley.

—Nathaniel Rakich, 538

In a February poll from Suffolk University/USA Today, likely South Carolina GOP primary voters were asked the most important issue facing the country. Of the options offered, 42 percent said that “immigration and border security” is the most important issue, 26 percent said “the economy” and 13 percent said the “future of American democracy.” No other issue offered got more than 5 percent of respondents.

—Mary Radcliffe, 538

The Republican presidential primary started out in territory pretty friendly to Haley. That changes after today, making the South Carolina primary a sort of last chance for the former Palmetto State governor to prove she actually has a path to the 1,215 delegates necessary to secure the GOP nomination. It looks somewhere between unlikely and impossible that she'll be able to pull that off.

It's all about the numbers. According to the polls, Trump leads Haley by about 30 points among likely Republican primary voters. But his delegate lead is what really matters — and it's likely to be even larger. That's because the South Carolina Republican Party awards its delegates on a winner-takes-all basis. About half the delegates will go to the winner of the statewide vote (almost certainly Trump) and the remainder will go to the winner of each of the state's seven congressional districts. With a 30-point statewide victory, Trump would probably win every district resoundingly; in 2016, the largest difference between Trump's statewide margin (10 points) and his margin in the most anti-Trump county (which he lost by 5 points to Marco Rubio) was only 15 points.

This is all disastrous news for Haley, who needs all 50 delegates from the state to be on track to win the Republican nomination. The competition on and after Super Tuesday will be even tougher. According to the math powering 538's delegate benchmarks, Trump is leading Haley by around 57 points in California and 69 in Texas, the states with the largest delegate hauls on Super Tuesday. Those states also allocate delegates on a winner-takes-all basis, as long as a candidate wins at least 50 percent of the vote.

The primary, in other words, is functionally over. But because Trump has not yet clinched a majority of delegates, Haley's campaign technically has a chance of winning. It's just very, very low.

—G. Elliott Morris, 538

If you are looking for something to listen to while we wait for polls to close and results to come in, allow me to suggest our latest episode of the 538 Politics podcast. We talk about what to expect tonight, including how South Carolina's primary electorate is different from that of other early states and how the results might shape what Haley does next. We also had a debate about a recent poll on presidential greatness and looked at polling that suggests the wars in Ukraine and Gaza have created some significant divides within the two parties.

—Galen Druke, 538