Live Updates: Voting Is Underway in South Carolina for the G.O.P. Primary

How quickly will the race be called?

As we saw in the Iowa caucuses and New Hampshire primary last month, the speed of a race call can give the victor — in both of those cases Mr. Trump — a sense of momentum, even an air of inevitability. Iowa was called for Mr. Trump before the caucuses had even ended.

Polls in South Carolina will close at 7 p.m., and Ms. Haley is expected to speak in Charleston once the winner is declared. The Trump campaign will hold a “watch party” in the state capital of Columbia, where the former president is expected to speak.

An early night for the two remaining candidates will say a lot about where the race is heading as they turn to Michigan next week ahead of Super Tuesday on March 5, when 15 states will vote to award 874 of 2,429 Republican delegates.

Can Nikki Haley outperform the polls?

If the contest results in the drumming that polling suggests it will, Ms. Haley, once thought to be South Carolina’s political star, is about to be trounced. Polling averages have her trailing Mr. Trump by 30 percentage points.

Just after the New Hampshire primary, Mark Harris, the chief strategist for Ms. Haley’s super PAC, SFA Fund, said that the former governor did not have to win her home state but that she did have to exceed her share of the vote in New Hampshire — 43 percent — to show she is making progress with Republican voters.

Betsy Ankney, Ms. Haley’s campaign manager, walked that back on Friday, saying: “We have never gotten into those benchmarks. We won’t start now.” But short of a victory, Ms. Haley needs to take some kind of consolation prize from the state where she was born, raised, served as governor and still lives.

Ms. Haley has said resolutely that she will stay in the race, regardless of the outcome in South Carolina. Still, she would like to exceed expectations so that she can remind voters of her favorite campaign T-shirt, ”Underestimate me. That’ll be fun.”

Will turnout and general disaffection with the choices matter?

Poll after poll has found that most Americans do not relish a rematch between President Biden and Mr. Trump, the major party nominees in 2020. Mr. Biden won the Democratic primary in South Carolina on Feb. 8 with more than 96 percent of the vote. But only 131,302 people voted, on the low end of an expected turnout that was always forecast to be anemic.

Unlike Iowa, where subzero temperatures and blowing snow most likely held down turnout, the weather in South Carolina will be fine on Saturday — gorgeous even. A low turnout could be attributed to the lack of drama in the state: Even Ms. Haley’s supporters evince little confidence that she could win. But a poor showing of South Carolinians could add a data point to Ms. Haley’s contention that Americans are desperate for a fresh, younger face to vote for in November — or more broadly, the point that none of the candidates have inspired voters in a surly mood.

How will the Lowcountry go?

South Carolinians like to divide themselves into three sections: the Upstate around Greenville and Spartanburg, where the question is, what church do you belong to?; the Midlands, dominated by the state capital, where the question is, what agency do you work for?; and the mellower Lowcountry of Charleston and the coast, where the question is, what do you drink?

Mr. Trump’s strength will be with evangelical conservatives in the Upstate, and his dominance with elected state officials in Columbia is a testament to Ms. Haley’s weakness in the Midlands, either because of the feathers she ruffled as governor or the tendency of politicians to side with the favorite.

That leaves the Lowcountry, where affluent Republicans fix up 19th-century mansions in Charleston and Beaufort, golf on Hilton Head or build sumptuous beach houses in the Charleston suburbs of Isle of Palms and Sullivan’s Island — and where Ms. Haley lives, on Kiawah Island. The Lowcountry should be Haley country.

But a surge of newcomers — the largest cohort from New York and New Jersey — has swelled more middle-class, inland suburbs around Charleston, as well as in Horry County, home to Myrtle Beach. They were not around for Governor Haley.

How this region votes will speak to Mr. Trump’s appeal with the educated, affluent Republicans who once controlled the party, and with suburbanites not influenced by their prior experience with Ms. Haley.