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

The polls are now closed in South Carolina, and based on an analysis of the exit polls, ABC News is projecting that Trump has won the state’s Republican primary. We’ll be sticking around for a while yet, though, to see what the exact margin is, how many delegates Trump will win and whether Haley will drop out following this decisive defeat.

—Nathaniel Rakich, 538