What to Watch in the South Carolina G.O.P. Primary

South Carolina voters head to the polls on Saturday to cast ballots in a Republican presidential primary that could well determine the political fate of the state’s former governor, Nikki Haley, in her long-shot bid to derail former President Donald J. Trump’s march to the Republican nomination.

Here is what to watch in the Palmetto State as votes are tallied Saturday night.

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.

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.