In an interview with the BBC, Mr. Biden said that former President Joseph R. ⁠Biden Jr.’s prostate cancer had spread into his bones and was causing pain.

Mr. Miller, who has faced pressure from fellow Republicans to end his campaign and avoid endangering a solidly red seat in Ohio, will stay in the race, his spokeswoman said.

The summer exit confirmed what had been apparent for weeks: that Republicans lacked the votes to pass the voting restrictions the president has made a top priority.