As voters prepare to head to the polls Saturday in South Carolina’s Republican primary, a survey released Friday showed increasing support for Texas Sen. Ted Cruz with front-runner Donald Trump’s numbers falling.

The Wall Street Journal/NBC News/Marist poll of likely Republican primary voters showed Trump's 16-point lead from January cut to a five-point advantage on the eve of the primary. Trump had the support of 28 percent of likely voters, while Cruz had 23 percent in the latest poll.

The poll showed that in the past few weeks Trump had lost support among nearly every group – especially those who consider themselves to be "very conservative,"  according to a story from CBS News.

Sen. Marco Rubio, (R-Fla.), was third in the poll with 15 percent of the vote, and former Florida Gov. Jeb Bush came in fourth with 13 percent.

The winner of the GOP South Carolina primary will get a big boost in the delegate count heading into Super Tuesday on March 1, as he will pick up at least 29 delegates.

Here is what you need to know in advance of Saturday’s primary:

What type of primary does South Carolina have?

The South Carolina Republican primary is an open primary, meaning  any registered voter can participate, voting for any candidate, regardless of the voter's political affiliation. For instance, a registered Democrat could vote for a candidate on the Republican ticket.

Is South Carolina a winner-take-all state?

Not exactly, but close. Twenty-nine of the 50 GOP delegates up for grabs go to the winner of the primary, then three delegates are awarded to the winners of each of the state's seven congressional districts. Mathematically, the winner  of the state would have to win at least some of the congressional districts, so the winner will get more than the outright 29 delegates.

When are the polls open Saturday?

From 7 a.m. until 7 p.m.

Is there anything else unique to South Carolina’s primary?

  • The Republican and Democratic primaries are on separate days. The Republican primary is on Feb. 20; the Democrats on Feb. 27.
  • The majority of South Carolina's population is white, (more than 2-1). The overwhelming majority of registered Republicans are white,  (10-1). The majority of registered Democrats are African American, making up more than 50 percent of registered Democrat voters.
  • The first presidential primary in South Carolina was held by the Republicans in 1980.