I'm on the fence. As I pointed out, this would be panic-time for a sitting president running for reelection — evidence of a significant rift in the party. And it's not a mystery what that rift is — people in the Republican party who have reservations about Jan. 6, Trump's electability or his presidential temperament. At the same time, he has majority support in most polls, far outpacing any rivals.

—Julia Azari, 538 contributor

The first few primaries to me don’t seem to suggest the kind of strength that I would expect from a universally known, pretty well-liked (within his party) former president. So, is Trump doing well in this race, or is he just doing better than Haley? And does that mean anything for November?

—Mary Radcliffe, 538

The South has historically been a politically distinct region. This distinctive character — associated for a long time with strong, conservative Democratic affiliation — has been really important in explaining how the Democratic presidential nomination calendar has evolved. Super Tuesday was initially pushed to strengthen Southern influence and give an advantage to moderate candidates. South Carolina itself was moved to a more prominent spot in the primary calendar because many of its Democratic primary voters are African American — unlike in the traditional early states of New Hampshire and Iowa.

But what does this mean for Republicans? The South has been a Republican stronghold for most of the twentieth century, though Democratic presidential candidates have pulled off occasional victories. And South Carolina hasn't been a distinctly regional primary for Republicans (though Georgian Newt Gingrich won the GOP primary there in 2012). Nikki Haley doesn’t seem to be enjoying much home state (or region) advantage there. And Trump, who is from New York, is consistently popular in the South.

The larger point here is probably that, now that it’s generally in the Republican column, the South has been much less exemplary of unique regional politics, and instead has similar issue positions and priorities as other Republican strongholds.

—Julia Azari, 538 contributor

Only a third of the estimated vote is counted so far, but Trump is leading Haley only 59 percent to 40 percent. If that 19-point lead holds, it would be a pretty far cry from the 28-point lead that the polls foresaw, even though they “called” the correct winner. It’s a good reminder that polls of presidential primaries historically have a lot of error.

—Nathaniel Rakich, 538

It's not a huge surprise that Haley thinks she can win tonight despite the odds. Her first political success was in a 2004 South Carolina state House Republican primary, in which she unseated a powerful 30-year incumbent to win. She tells that story on the stump, and the message is clear: She's won as an underdog before.

As a legislator, Haley carved out a reputation in South Carolina as an outsider taking on state power. She sponsored a bill to force roll call votes on issues like raising legislator pay, losing support from her colleagues and a race for a committee chair position in the process. Later, as governor, she became known for luring businesses to the state, siding with business over labor, signing a 20-week abortion ban and blocking Medicaid expansion.

On social issues, though, she has tried to walk a middle path. Haley has talked about the racism her Indian American family faced in rural South Carolina, and supporters have said the "good ol' boys" network never quite accepted her in state politics. But she also frames her success as an example of how the South has made progress. She didn't tackle the issue of the Confederate battle flag flying over the State House until after a racist shooting in Charleston in 2015, in which nine churchgoers were killed in Emanuel AME Church. She has also sidestepped more recent controversies, like anti-transgender bathroom laws.

Of course, all of her history in the state hasn't seemed to help her against Trump. In polls, she's winning only about a third of potential voters. She may be used to playing the role of David, but not all Goliaths fall in defeat.

—Monica Potts, 538