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

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