Rep. James E. Clyburn (D-S.C.) (Photo by Chip Somodevilla/Getty Images)

LAS VEGAS -- Rep. James E. Clyburn, whose endorsement is the most coveted in the battleground state of South Carolina, will endorse Hillary Clinton on Friday, according to two Clinton campaign sources.

Clyburn, considered the kingmaker of Democratic politics in the state, had insisted until recently that he would remain neutral in the primary race with Clinton and Vermont Sen. Bernie Sanders.

But he told The Washington Post in a recent interview that under intense pressure from his friends and family, he was reconsidering his pledge.

“That was certainly my intention,” Clyburn  said of his initial plan to remain neutral. “But I am re-evaluating that. I really am having serious conversations with my family members.”

The Clinton campaign announced a "momentous" endorsement scheduled for 11 a.m. in Columbia, S.C., Friday.

The endorsement comes just over a week before the South Carolina primary, a contest where Clinton currently holds a double-digit lead over Sanders.

Before then, however, the Nevada caucuses loom on Saturday and polls show that despite having a long-standing campaign presence in the state, the contest is a dead heat.