What to know about the South Carolina Republican presidential primary

South Carolina's Republican presidential primary kicks off on Saturday, and only two major candidates are left to duke it out: former President Donald Trump and former U.N. Ambassador Nikki Haley.

So with the primary set to get underway, here's what to know about where the candidates, who can vote and the state's record for picking the eventual nominee.

How does South Carolina's primary work?

South Carolina has an open primary, which means registered voters can cast a ballot in either the Democratic or Republican primary. Unlike Iowa and New Hampshire, South Carolina does not require voters to register by party, however residents are allowed to vote in only one of the primaries.

Despite its open primary, the state has many more active Republican voters than Democratic ones. And it doesn't have New Hampshire's tradition of independent voters swinging back and forth.

Over the summer, South Carolina's Republican Party moved its primary so that it is 18 days after Nevada's caucus, allowing candidates nearly three weeks to saturate the state.

The primary is traditionally held on a Saturday and, unlike New Hampshire, allows for early voting beginning in mid-February.

Already, about 205,000 ballots have been cast in the two-week window to early vote and 12,000 absentee ballots have been returned for a total count of roughly 217,000 ballots, according to the state's election commission. In 2020, there were about 500,000; in 2016, there were about 260,000, the election commission reported.

Where do the candidates stand?

It has been a bumpy road for Haley. She placed a distant third in the Iowa caucuses in January, she finished second behind Trump in New Hampshire and lost to "None of the Candidates" in Nevada's primary.

Trump holds a wide 30-point lead over Haley, the former two-time South Carolina governor, according to 538's national polling averages. Haley, looking to close that gap, has spent the past few weeks crisscrossing the state on her "Beast of the Southeast" tour, visiting some 25 counties in the process.

Despite the bleak odds that she can overtake the former president in her home state, Haley told voters at a rally in Greenville earlier this week that she has "no fear of Trump's retribution" and will continue to fight on.

Since 1980, South Carolina's Republican primary has gone on to pick the Republican nominee, with one exception: in 2012 with Newt Gringrich (Mitt Romney went on to become the GOP nominee that year). Winning, or the margin by which she loses, could very well be a good indicator on whether or not Haley stands an actual chance against Trump.

The state has a large number of conservative and evangelical voters -- and Trump, in the past, has appealed to that base. In 2020, he won the state by 55% and in 2016 by 54%, according to the state's election commission.

How an open primary could affect the contest

Exit polls in New Hampshire showed Haley doing especially well with undeclared voters -- a group that was able to vote in the state's Republican primary. She also received strong backing from self-described moderates, just as she did in the Iowa caucuses, where she won about one-third of self-described independents, exit polling found.

Haley has encouraged "as many people" that are willing to cast their ballots to vote on Saturday.

"I'm going to be serving everybody, so whoever cares enough about this election and wants to be involved -- we want their support."

But Republicans and Democrats have commented on voter participation in the open primary.

"The South Carolina Republican Presidential Preference Primary has the best track-record in the country for picking presidents, and I'm not going to sit back and allow Democrats to tarnish our reputation," Chairman of the South Carolina Republican Party Drew McKissick said in a statement.

As early voting continues through Feb. 22 in South Carolina, Jay Parmley, executive director of the South Carolina Democratic Party, sent out an email on Monday warning that those who vote in the Republican presidential primary can't also take part in the upcoming county-level Democratic conventions.

"I fielded a tons of phone calls at the state party office from Democrats who are saying I really think I'm gonna go vote in that Feb. 24 Republican primary because I'm gonna go for Nikki Haley. And I'm going to stop Donald Trump votes. That is stupid," Parmley said. "Donald Trump is on his own trajectory on the Republican side, and Nikki Haley, she is the mother of MAGA -- she was MAGA before they even had a definition. And I tell Democrats all the time, if you didn't vote for her for governor, why in the world would you go vote for her to be the Republican nominee for president? She is just as dangerous."