South Carolina holds its Democratic primary Saturday and Republican voters could throw a wrench into the contest that is seen as a must-win for former Vice President Joe Biden.

Here are five things to watch for on Saturday.

Will Joe Biden's firewall hold up?

Most polls in recent days have Biden winning the primary, some by double digits. This is mainly buoyed by his support among African-Americans, who will make up a large percentage of voters Saturday. He received an endorsement this week by South Carolina Rep. Jim Clyburn.

A Biden win would not only be seen as a huge boost to his chances of at least making it to the convention in July, it would also be his first-ever primary contest win in three tries running for president. But a second-place finish -- even by one-tenth of a percent -- could be seen as an unrecoverable loss.

RELATED: Most voters think Barack Obama endorsed a candidate. He hasn't.

RELATED: Iowa to certify caucus results Saturday

Will Republican 'chaos' help Sanders?

If Sen. Bernie Sanders does win, he may have Republicans to thank. A pair of movements in the Palmetto State are urging GOP voters to take part in the Democratic primary and cast ballots for the Vermont senator. One of them is called "Operation Chaos."

The South Carolina Republican Party canceled its primary and is giving its delegates to President Donald Trump by default. So, Republican voters are free to vote in the Democratic primary -- and are being encouraged to do so. 

Both movements are targeting Sanders, believing he would be the weakest candidate to take on Trump in November.

Sanders is already projected to win the majority of the 14 states on Super Tuesday. If he previews that with a win in South Carolina, he will have won the popular vote in the first four contests -- something no one has ever done. It would only boost his momentum and could make him unstoppable.

Steyer spoiler?


Businessman Tom Steyer has put millions into trying to win South Carolina. Polls show he's not expected to do so, but some of them suggest he could push Sanders to third place in the state and maybe even prevent the senator from winning any delegates.

Based on how the polls look, it's about even-money as to whether Steyer will walk out of South Carolina with his first pledged delegates of the race.

Can Warren bounce back?

After her third-place finish in Iowa, Sen. Elizabeth Warren finished fifth and fourth, respectively, in New Hampshire and Nevada. A strong finish in South Carolina would be a big boost headed into Tuesday, but a polling average by fivethirtyeight.com has her finishing sixth. She's tied for fourth with in a RealClearPolitics poll analysis.

Regardless, don't expect her to drop out no matter what happens Saturday. Politico reports a Super PAC just dropped $9 million in ad money in her home state of Massachusetts, plus California and Texas, for Super Tuesday.

Can Buttigieg and Klobuchar break through with African-Americans?

Pete Buttigieg's delegate win in Iowa, his close second-place finish New Hampshire and Klobuchar's surprise third-place New Hampshire finish gave them fundraising boosts and shot of early life in their campaigns. But the Nevada caucuses came -- a much more racially diverse state -- and they finished a distant third and sixth, respectively. 

Most polls ahead of the vote have them in single digits in South Carolina (Buttigieg is in the low teens in a few). Their support with African-Americans -- who will be prominent in this contest -- is generally even lower.

But, surprises have happened before.