South Carolina Rep. James Clyburn (D) will reportedly endorse former Vice President Joe Biden Joe BidenMomentum growing among Republicans for Supreme Court vote before Election Day Trump expects to nominate woman to replace Ginsburg next week Video of Lindsey Graham arguing against nominating a Supreme Court justice in an election year goes viral MORE for the Democratic nomination on Wednesday, days before the state's primary, which is a crucial test for the Biden campaign.

Politico reported the impending endorsement Sunday afternoon. Clyburn himself told NBC's "Meet the Press" on Sunday that he would endorse later in the week, while not revealing his pick.

“I will endorse Wednesday morning,” Clyburn told NBC. “I’m going to tell everybody who I’m going to vote for. I’m just not going to do it today.”

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The House majority whip and a member of the Congressional Black Caucus, Clyburn carries significant weight in the South Carolina primary. The state is seen as a major test for Democratic candidates as they seek the support of African American voters.

Biden faces a crucial moment in the state after disappointing finishes in the Nevada caucuses on Saturday, trailing Sen. Bernie Sanders Bernie SandersNYT editorial board remembers Ginsburg: She 'will forever have two legacies' Two GOP governors urge Republicans to hold off on Supreme Court nominee Sanders knocks McConnell: He's going against Ginsburg's 'dying wishes' MORE (I-Vt.) by more than 20 points. He suffered defeats in Iowa and New Hampshire as well, where the former vice president trailed former South Bend, Ind., Mayor Pete Buttigieg Pete ButtigiegBipartisan praise pours in after Ginsburg's death Bogeymen of the far left deserve a place in any Biden administration Overnight Defense: Woodward book causes new firestorm | Book says Trump lashed out at generals, told Woodward about secret weapons system | US withdrawing thousands of troops from Iraq MORE (D).

Biden's campaign did not immediately return a request for comment Sunday evening from The Hill.