Dick Durbin, the longtime second-ranking Democrat in the Senate, announced plans to retire at the end of next year, setting off a succession scramble to take his powerful leadership spot in the chamber and a likely crowded primary in Illinois for the seat.

Senator Richard J. Durbin’s departure will set off a primary for a rare open Senate seat in Illinois and open a top leadership slot. He said it was time to “face reality” and make way for someone new.

Ill., announced Wednesday that he will not seek reelection in 2026 and will retire after serving for over four decades in Congress.