(CNN) Rep. Jim Clyburn, the highest-ranking African American in Congress and an influential figure in South Carolina politics, endorsed former Vice President Joe Biden on Wednesday.

Clyburn's endorsement comes ahead of Saturday's South Carolina primary, where Biden needs a win in order to keep his bid for the Democratic presidential nomination alive.

"I know Joe Biden. I know his character, his heart, and his record. Joe Biden has stood for the hard-working people of South Carolina. We know Joe. But more importantly, he knows us," Clyburn tweeted ahead of a news conference about his endorsement. "In South Carolina, we choose presidents. I'm calling on you to stand with @JoeBiden."

The endorsement was no surprise, but it was still an important one for Biden. His support among black voters in South Carolina -- and, Biden hopes, across the South, where several other states are among the 14 that vote three days later on Super Tuesday -- is his most campaign's most important asset. Biden has called South Carolina his "firewall."

Clyburn had long said he knew who he would be voting for but refused to make his plans public. He said he decided to endorse Biden publicly after an elderly woman told him Friday at a funeral, "I've been waiting to hear from you."

"I want the public to know that I am voting for Joe Biden. South Carolina should be voting for Joe Biden," Clyburn said at a news conference in North Charleston.

Clyburn said he'd gotten to know Biden when the two were in Congress and that early on they'd discussed the landmark Supreme Court decision Brown v. Board of Education that desegregated public schools. It was a case that combined five individual cases -- including one from South Carolina and one from Biden's home state of Delaware.

"I know Joe. We know Joe. But most importantly, Joe knows us," Clyburn said.

"I know his heart. I know who he is. I know what he is. I know where this country is: We are at an inflection point," Clyburn said. "I am fearful for the future of this country. I'm fearful for my daughters and their future, and their children and their children's future."

"It is time for us to restore this country's dignity, this country's respect," he said. "That is what is at stake this year. And I can think of no one better suited, better prepared -- I can think of no one with the integrity, no one more committed to the fundamental principles to make this country what it is -- than my good friend, my late wife's great friend, Joe Biden."

Speaking to CNN's Wolf Blitzer on "The Situation Room" later Wednesday, Clyburn expanded on his praise of Biden, specifically highlighting his "comfort levels with dealing with diverse issues."

When asked if a one-point victory in the South Carolina primary would be enough to propel Biden's campaign, Clyburn said bluntly, "One point may be a win, but I don't think it's ... the propelling that we need."

"I want to see a much bigger victory than that. I want South Carolina to play its usual role," he said. "When Bill Clinton came to South Carolina, he had lost eight contests, and we propelled him into the presidency. When Barack Obama came to South Carolina, he had just lost New Hampshire the week before, and lost it big. But we propelled him into the nomination and the presidency."

Clyburn added: "So I want to see a big vote for Joe Biden because I think it will propel him into the nomination and the presidency."

Biden heaped praise on Clyburn earlier Wednesday morning during a speech at a National Action Network breakfast hosted by the Rev. Al Sharpton. He credited Clyburn with helping the Obama administration enact the federal stimulus package and the Affordable Care Act.

After Clyburn's endorsement, Biden took a thinly veiled swipe at Vermont Sen. Bernie Sanders, the Democratic presidential front-runner who has closed the gap with Biden in South Carolina polls.

"Today people are talking about a revolution," Biden said at the news conference where Clyburn announced his endorsement. "What the country's looking for are results. What they're looking for is security. What they're looking for is to be able to sustain and maintain their dignity."

Biden pointed to South Carolina's history of launching Democratic presidential hopefuls toward the nomination.

"South Carolina chooses presidents," Biden said. "You decided to launch Bill Clinton to the White House. ... You launched my buddy Barack Obama to the White House. And I firmly believe once again on Saturday, you hold in your hand in South Carolina the power to choose the next president of the United States. And I'm here, heart and soul, with everything I've got, to earn the support of the people of South Carolina."

"I promise you this: If you send me out of South Carolina with a victory, there'll be no stopping us," he said. "We'll win the nomination, we'll win the presidency, and most importantly, we'll eliminate the fear so many have in this country of a second term of Donald Trump."

This story has been updated with additional information.