For the purposes of this analysis, I think we should view Trump as an incumbent when measuring his performance in the primary. Republican voters know exactly what Trump is like in the White House, and they can judge for themselves how he did on the issues they care about (he generally does well on this axis) and his character (things are more muddled here).

If we think of him as an incumbent, he is doing quite poorly. Remember how Pat Buchanan embarrassed H.W. Bush by getting 38 percent of the vote in New Hampshire in 1992 and is blamed for weakening him for the general? Haley has been doing better than Buchanan across the early states. There are plenty of Republican voters who don't think of Trump as ideal. We've probably all heard their arguments. Something along the line of, "his character isn't ideal, but he fights for me."

Now, what does this all mean for the contest against Biden in the fall? Not much. The vast majority of those people will vote for Trump in the fall. And if we are sticking with the 1992 comparison, Bill Clinton was a popular candidate (net +11 favorability in September of '92). Joe Biden is not. His favorability rating is currently at net -15 points. So, Trump is doing poorly, but so is Biden. When it's a race to the bottom all around, doing poorly in a GOP primary doesn't tell us all that much.

—Galen Druke, 538

I see your point, Mary — Trump has gotten “only” around 50-60 percent in the first three contested states — but I think in the grand scheme of things, that’s still a strong performance. Iowa winners much more often finish in the 20s or 30s, and New Hampshire is just weird because of its demographics and high proportion of independent voters. And at the end of the day, he’s the first non-incumbent Republican to win all three of Iowa, New Hampshire and South Carolina, and there’s a good chance he’s going to win all 56 contests.

—Nathaniel Rakich, 538

For a non-incumbent (if former president), Trump has made short work of the primary calendar, basically annihilating any real competitors in record time without ever having to deign to step foot on a debate stage. The fact that he didn’t completely cruise to the nomination captures some of the hesitancy in the party that Julia highlighted, but at the end of the day, all Trump needs to do now is be more popular than Biden, who isn’t exactly the Prom King these days.

—Kaleigh Rogers, 538

I'm honestly not sure there is a clear way to go about establishing what Trump "should" be winning, Mary. On the one hand, polls had him at 61 percent, so 60 percent of the vote (as of now) is pretty good — especially if you consider he'll win the nomination easily by mid-March if this is the case.

Another benchmark would be the percent of the GOP electorate that calls themselves "part of the MAGA movement." According to preliminary ABC exit polls, that's about 44 percent of SC voters (50 percent said no and 6 percent were unsure). So by this benchmark, Trump is actually overperforming.

Too bad there aren't a whole lot of modern examples of former presidents + failed presidential candidates running in subsequent primaries, or else we could try to establish historical baselines. Trump's performance right now is somewhere between George H.W. Bush vs. Pat Buchanan and Jimmy Carter vs. Ted Kennedy. Both of those incumbents lost in the general.

—G. Elliott Morris, 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