South Carolina Rep. James Clyburn, the third-ranking Democrat in the U.S. House of Representatives, is endorsing Barack Obama for president, his office said on Monday.

Clyburn, the highest-ranking black member of Congress and a delegate to the August nominating convention, plans a formal endorsement of the Illinois senator on Tuesday and is urging the state’s other uncommitted delegates to rally around Obama.

Obama won the South Carolina nominating contest in a landslide in January, and is edging closer to clinching the Democratic presidential nomination after a hard-fought battle with rival Hillary Clinton.