We’re less that 24 hours from the most important contest to date in the 2012 presidential race: South Carolina’s Republican presidential primary.

Below is what you need to know about the vote to come.

* Why is South Carolina important?

Because it picks presidents (as the saying goes).

While Iowa’s caucuses can lay claim to being first vote of the presidential race and New Hampshire is proud of its first-in-the-nation primary, South Carolina has traditionally been the place where winners win. While the other two have spotty records on this front, South Carolina has picked every Republican nominee since its front-of-the-calendar primary began in 1980.

This is because, with the first two states often splitting their vote between two candidates (one winning Iowa and one winning New Hampshire), South Carolina has been the de facto tie-breaker, setting the winner on a course for victory.

Ronald Reagan, George H.W. Bush, Bob Dole, George W. Bush and John McCain all split Iowa and New Hampshire with another candidate before South Carolina sent them off on a winning streak that resulted in the nomination. Few of them ever looked back after the Palmetto State, going on long winning streaks soon after.

Indeed, now that it looks like Mitt Romney may not have actually won Iowa, it appears South Carolina will again be the rubber match in the GOP presidential candidate.

*Who votes in South Carolina?

While the state is stereotyped as very Southern and very conservative, it’s not quite so simple.

Many forget that independents can vote and have a lot of say over who the nominee is. The electorate isn’t as moderate as, say, New Hampshire, but given that there is no competitive Democratic primary, independents really only have one contest to cast ballots in. That’s why former Utah governor Jon Huntsman’s exit earlier this week was seen as a boon to Romney, who can pick up whatever moderate voters Huntsman might have been able to nab.

In 2008, Sen. John McCain (Ariz.) lost to former Arkansas governor Mike Huckabee narrowly among Republicans but carried independents by a wide margin, winning him the state. That said, less than one in five voters in the 2008 GOP primary was an independent.

In addition, the recent influx of out-of-state retirees to the coastal areas of the state means the electorate isn’t as Southern as it once was.

Indeed, even as Iowa has often picked the more conservative insurgent candidates, South Carolina has often picked the more moderate establishment favorite.

In addition, the state has repeatedly elected Sen. Lindsay Graham (R-S.C.) – not exactly a conservative favorite – and has also sent some more moderate Republicans like former congressman Bob Inglis to Congress (even though Inglis lost a primary in the year of the tea party in 2010).

One thing working against Romney: The evangelical vote. Exit polls from 2008 showed six in 10 GOP primary voters described themselves as evangelicals, and Romney continues to under-perform among this group — a fact that likely cost him a clear win in Iowa.

A CNN/Time/Opinion Research poll of South Carolina primary voters released this week showed Romney winning 47 percent of non-evangelicals, but just 26 percent of evangelicals.

Why is the vote held on Saturday?

A few primary states and several caucus states just happen to hold their contests on Saturdays.

South Carolina has done this every year its held its primary, except in 2004 when it was held on a Tuesday. Election law does not require that the race be held on a Saturday.

Other states holding their contests on Saturdays this year include the Nevada caucuses (Feb. 4), Washington state caucuses (March 3), Kansas caucuses (March 10), Missouri caucuses (March 17) and Louisiana primary (March 24).

Some argue that holding the contests on Saturdays allows for higher turnout, since people don’t have to work on the weekends. They also make it so these states don’t have to share a primary date with another state, as most Tuesdays feature multiple contests in other states.