CHARLESTON, S.C. — Former Vice President Joe Biden will finish second in the Nevada Democratic presidential caucuses, NBC News projected Sunday night, and will likely earn seven national convention delegates.

The second-place finish, added to the endorsement of South Carolina's top Democrat, Rep. Jim Clyburn — which will come Wednesday, NBC News has learned — will give Biden momentum heading into this week's South Carolina primary.

Biden had polled 20.9 percent of the votes in Nevada with nearly 88 percent of precincts reporting. Biden will finish well behind Sen. Bernie Sanders, I-Vt., who had 47.1 percent on Sunday evening. Pete Buttigieg, the former mayor of South Bend, Indiana, was third, with 13.6 percent.

Candidates have to hit 15 percent both statewide and in congressional districts to receive a share of Nevada's 36 pledged delegates to the Democratic National Convention. Sanders won 18 delegates, Biden seven and Buttigieg got two.

Biden started the Democratic campaign as the front-runner, but after stumbles in Iowa and New Hampshire, he had raised the stakes for Nevada and South Carolina amid heightened concerns about the stability of his candidacy. The outcome in Nevada could buttress the campaign's argument that he has unique appeal with minority communities, especially moving forward to what Biden once considered his "firewall" in South Carolina.

Recent polls have shown Biden losing significant support among African Americans in South Carolina to Sanders and billionaire Tom Steyer. Biden has heightened his attacks on both in recent days.

Official backing from Clyburn, colloquially known as the "South Carolina Kingmaker" for his heavy influence in the state's Democratic politics, could help cement what Biden has predicted would be a first-place finish in South Carolina. Clyburn, who as majority whip is the third-ranking Democrat in the House, will formally endorse Biden ahead of the primary at an event Wednesday, according to two people with firsthand knowledge.

He is the highest-ranking person in House leadership to have backed Biden's candidacy to date.

In a live interview with MSNBC's Kasie Hunt on Sunday night, Biden said he was unaware of Clyburn's backing being made official, adding that it would be "the single most valuable endorsement."

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Clyburn has gone out of his way at times to praise Biden and to talk positively about his chances here while insisting that he hadn't picked anyone in the race.

He spoke at a Biden event just last month but insisted that he still hadn't endorsed. Clyburn said recently that his commitment to the party was to withhold an endorsement until after Tuesday's debate, which is co-sponsored by the Congressional Black Caucus.

Rep. Cedric Richmond, D-La., a co-chair of Biden's campaign, said in a statement that he was unaware of Clyburn's preference.

"Congressman Clyburn is my mentor and one of my closest friends. He has not indicated to me who he is going to endorse. I hope it's Joe Biden and know they have a relationship. He has said to me the future of the country is at stake, and if we lose to Donald Trump, it would be devastating for generations of African-Americans to come. And I know that's what he's thinking about when making this important decision."

Clyburn's support for Biden goes back years; he hinted that he would support the vice president's candidacy as far back as 2018. Asked last week about Biden's chances, Clyburn told NBC News, "If the election were held tomorrow, he would win."

But it's been clear over the past few months that he's less sure that Biden will put up a resounding win. In multiple interviews, Clyburn has spoken about the qualities of other Democrats in the race.

Clyburn said Sunday on "Meet the Press" that Sanders "brings a lot to the table for people to consider" before warning that "anybody who refers to themselves as a democratic socialist — that word has always had really dire consequences throughout South Carolina."