House Majority Whip Jim Clyburn (D-SC) is planning to endorse Joe Biden (D) later this week, a move meant to fortify the former vice president’s South Carolina firewall as it crumbles to pressure from Sen. Bernie Sanders (I-VT).

Clyburn, who is the highest ranking black member of Congress, reportedly sees his endorsement of Biden as a “last-ditch effort to blunt Bernie Sanders’ momentum,” according to Politico. The endorsement is likely to galvanize South Carolina’s black voters, who will make up more than two-thirds of the Democrat primary electorate.

Although the endorsement has not yet been publicly confirmed, Clyburn strongly hinted at his preference during a Sunday appearance on ABC’s This Week.

“I do believe it will be an extra burden for us to have to carry,” the majority whip said about the prospect of a Sanders’ nomination. “This is South Carolina, and South Carolinians are pretty leery about that title socialist.”

Clyburn’s likely intervention in the Democrat contest comes as Biden’s position in South Carolina, long thought to be his firewall, has deteriorated. Despite once leading his rivals in the state by double digits, the former vice president now finds himself with only a narrow lead over Sanders and environmentalist billionaire Tom Steyer. Biden’s newfound standing comes after back-to-back losses in Iowa, New Hampshire, and Nevada shattered his electability argument and drained an already lackluster fundraising operation.

All of that has been to the boon of Sanders, who after stringing together a diverse coalition to win the Nevada caucuses last week, is now the unbridled frontrunner. The Vermont septuagenarian’s campaign not only looks unstoppable in its march forward, but also stands a strong chance of winning South Carolina, much to the concern of members of the Democrat regulars, like Clyburn.