A wildcard in the looming South Carolina primary is about to play his hand.

Rep. Jim Clyburn (S.C.), the third-ranking House Democrat and a leading member of the Congressional Black Caucus (CBC), said Thursday that he plans to endorse either former Secretary of State Hillary Clinton Hillary Diane Rodham ClintonHillicon Valley: FBI chief says Russia is trying to interfere in election to undermine Biden | Treasury Dept. sanctions Iranian government-backed hackers The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters FBI chief says Russia is trying to interfere in election to undermine Biden MORE or Sen. Bernie Sanders Bernie SandersMcConnell accuses Democrats of sowing division by 'downplaying progress' on election security The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters Why Democrats must confront extreme left wing incitement to violence MORE (I-Vt.) before the Palmetto State's Feb. 27 vote.

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"It'll be after this weekend," Clyburn told a horde of reporters in the Capitol.

Clyburn said he doubts he'll meet with either candidate before he announces his decision, choosing instead to huddle with family and political friends at home.

The move marks a shift for Clyburn, who declined to endorse a candidate through most of the 2008 primary, when Clinton lost the contest to then-Sen. Barack Obama Barack Hussein ObamaThe Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon Trump appointees stymie recommendations to boost minority voting: report Obama's first presidential memoir, 'A Promised Land,' set for November release MORE (D-Ill.). He entered 2016 with the intent of remaining neutral again.

But family pressures, he said, have sparked a change of heart.

"They said you need to make a stand," Clyburn said of his family. "They said whatever you're going to do, you need to do it."

Support from Clyburn would be a boon to either campaign, as both Clinton and Sanders are scrambling to attract African Americans ahead of the primary in South Carolina, where black voters constitute a significant bloc.

Both Clinton and Sanders have faced criticism from black activists on the campaign trail. The protesters have lobbed accusations that, despite liberal track records, neither candidate has done enough to prioritize race-based issues.

Rep. G.K. Butterfield George (G.K.) Kenneth ButterfieldCongress must protect kidney disease patients during the COVID-19 pandemic The time for HELP is now: Senate should pass bill to expedite recovery following natural disasters Rep. Clyburn on Confederate statues: Mob action is no answer MORE (D-N.C.), chairman of the CBC, said Clyburn's reputation in South Carolina would lend a huge boost to one of the contenders.

"Mr. Clyburn is so well respected in South Carolina," Butterfield said. "Anyone that he would endorse would get significant votes because of it."

Asked why it's taken so long to endorse, Clyburn said, "Because I don't want to damage my primary."

"I think I've said that now for 10 years, that I don't want to do anything that would jeopardize South Carolina not being in the [early] primary window. And I don't want any candidate using me as an excuse not to show up in the state."

Clyburn on Thursday showered accolades on both Democratic hopefuls, hailing Clinton's work on healthcare reform as the first lady in the 1990s, and praising Sanders's influence on the Affordable Care Act in 2009 and 2010.

"Like Sen. Sanders, she has a great record to lay out before the American people," Clyburn said in an interview with CNN. "And so we're going to be discussing all of that this weekend with family and friends. And we're going to be guided by the advice I get from them."

Clyburn has given few hints about which way he's leaning. In fact, he's quick to note that the primary contest has already divided his own family.

"My youngest daughter is very much for Hillary. My oldest grandson is very much for Sanders," Clyburn told The Hill this week. "So we've got a split family."

In 2004, Clyburn initially backed Richard Gephardt in the Democratic primary race, then switched to John Kerry John Forbes KerryThe Memo: Warning signs flash for Trump on debates Divided country, divided church TV ads favored Biden 2-1 in past month MORE when Gephardt exited.

Clyburn will have plenty of company in South Carolina over the weekend, as a number of CBC members supporting Clinton are heading there to stump for the former secretary of State.

On Thursday, the CBC's political action committee, or PAC, officially endorsed Clinton with the message that she's the more experienced and pragmatic of the Democratic hopefuls.

"We must have a president who is knowledgeable on both domestic and foreign policy," Butterfield said in stamping the endorsement.

But the PAC’s announcement was not without some blowback, as the endorsement was quickly panned by Rep. Keith Ellison (D-Minn.), a CBC member who is backing Sanders. Ellison emphasized that the CBC PAC — which has only seven CBC members on its 20-member board — is a separate entity from the CBC.

"Cong'l Black Caucus (CBC) has NOT endorsed in presidential," Ellison tweeted. "Separate CBCPAC endorsed withOUT input from CBC membership, including me."

The distinction was not overlooked by House Minority Leader Nancy Pelosi (D-Calif.), who noted the controversy Thursday in her weekly press conference.

"It's significant to have the endorsement of a Congressional Black Caucus," she said. "But one of my colleagues, Mr. Ellison, has hastened to add that it's not an endorsement of the Congressional Black Caucus."

Clyburn's relationship with the Clintons has seen its share of controversy.

Amid the 2008 primary, Bill Clinton William (Bill) Jefferson ClintonD-Day for Trump: September 29 Trump job approval locked at 42 percent: Gallup If Trump doesn't know why he should be president again, how can voters? MORE angered many African Americans when he compared an Obama win in South Carolina to Jesse Jackson's victory there in 1988. The critics accused the former president of trying to belittle Obama's success in the race, and Clyburn joined that chorus, advising Bill Clinton to "chill a little bit."

Exacerbating the tensions, Bill Clinton launched accusations that Obama's team had "played the race card on me."

“When he was going through his impeachment problems, it was the black community that bellied up to the bar,” Clyburn told The New York Times at the time. “I think black folks feel strongly that that this is a strange way for President Clinton to show his appreciation.”

Clyburn recalled the saga in his 2014 memoir, "Blessed Experiences: Genuinely Southern, Proudly Black." He said Bill Clinton called him in the middle of the night with an unveiled threat: “If you bastards want a fight, you damn well will get one,” he wrote.

“He was very upset," Clyburn continued. "His wife had just suffered a major defeat in the South Carolina primary, and I had not been involved in it, but Bill Clinton thought otherwise."

Clyburn said this week that those conflicts are water under the bridge.

"Certainly people remember all that. But that's not going to be controlling," he told CNN.

"I never held that against Bill Clinton. I spoke out at that time because I thought I should," he added. "But I wasn't holding anything against him. I just offered an alternative opinion."