Haley spent a good portion of her speech attacking Trump and Biden in equal measure. It definitely raised the specter of a third-party candidacy down the line, after she loses the GOP nomination, perhaps on the No Labels ticket. Haley has said she’s “not interested in talking” with the centrist group, but that doesn’t mean she can’t develop an interest later on.

And it’s not entirely unheard of for a losing GOP candidate to launch a more center-minded independent bid for president against an incumbent Democrat and the Republican who beat them in the primary. Illinois Rep. John Anderson did just that in 1980 against Jimmy Carter and Ronald Reagan. He ultimately won about 6.6 percent of the vote (5,719,850 popular votes, but no electoral votes).

—Jacob Rubashkin, Inside Elections

That electability case may not be resonating with actual primary voters, though. According to a January poll conducted by Monmouth University/The Washington Post, likely South Carolina GOP primary voters care more about issues than electability in choosing their nominee. Sixty-two percent said it was more important to nominate a candidate whose positions on the issues are closest to their own, while 33 percent said it was more important to nominate a candidate who seems most likely to beat Biden in November. There was little difference between Trump and Haley voters on this: 61 percent of Trump voters and 64 percent of Haley voters said that issue positions were more important, while 34 percent of Trump voters and 31 percent of Haley voters chose electability.

—Mary Radcliffe, 538

Haley addressed supporters at about 8:30 p.m. Eastern, and vowed to stay in the race: "I said earlier this week that no matter what happens in South Carolina I would continue to run for president, and I’m a woman of my word," she said. Haley said she was frustrated and worried about the future of the country and the world, and that she was running to save it. "America will come apart if we make the wrong choices," she said. Again, Haley presented her case as one of electability. She said that we couldn't live with four more years of Biden's failures or Trump's lack of focus, and that the voters in future primaries deserved a choice, not a "Soviet-style election" with one candidate. With about 40 percent of the vote (as of now), she noted that it was roughly the same amount she'd gotten in New Hampshire. "I’m an accountant. I know 40 percent is not 50 percent," she said. "But I also know 40 percent is not some tiny group." Those people were looking for an alternative, and she said she shared their frustration. The electability argument is one that Republican primary voters aren't buying.

—Monica Potts, 538

Political scientist Seth Masket has some interesting graphs comparing Trump's 2024 county-level vote share — based on what we know so far — to his 2016 performance in those counties, and it tracks pretty well. Meanwhile, Haley's performance is strongly related to Rubio's in 2016 at the county level - but not so much to Ted Cruz's.

—Julia Azari, 538 contributor

I have become a little obsessed tonight about what we should be expecting Trump to hit in this primary a priori. That is, given Trump is assumed to be the eventual party nominee and almost universally liked in the GOP, should he be winning more than 60 percent in South Carolina?

I already gave my case for answering "no" to that question: Strictly speaking Trump is dominating the delegate count and running ahead of his 2016 vote share in most counties with complete counts this primary cycle. And if you consider that Haley gets a home-state advantage in South Carolina tonight, Trump's adjusted vote share is close to 65 or 70 percent; our delegate benchmarks think Trump should have won 68 percent of the vote based on the demographics of the state alone. That's not the highest number, but it's not the lowest right? Would 65 percent be "good" for Trump? 75 percent? 80?

One counterargument to this centers around how the media has covered historical performances by incumbent presidential candidates. Journalist Jill Lawrence points out that in 1992, Patrick Buchanan challenged incumbent President George H.W. Bush for the GOP nomination and won 40 percent in the New Hampshire primary, holding Bush to 58 percent of the vote. That's an almost identical split to the results from tonight. The New York Times journalist Robin Toner wrote up the results with the headline "BUSH JARRED IN FIRST PRIMARY" and said the result "amounted to a roar of anger" from Republican primary voters.

If Trump was a true incumbent, I imagine the news media would use a similar headline to describe tonight's results in South Carolina. Perhaps our expectations for him are too low, or we're too focused on the broader state of play? Haley said in her concession speech tonight that she will stay in the race indefinitely, so I guess we'll get more data on Super Tuesday — only 10 days from now. The primary lives on!

—G. Elliott Morris, 538