Seeking to revive his struggling reelection campaign, U.S. President Joe Biden held a rare rally in Detroit on Friday, telling a cheering crowd he wasn't going to leave the race and warning that Republican Donald Trump poses a serious threat.

Biden, 81, is trying to shift the conversation from his mental sharpness and a growing number of Democratic defections to the impact of another Trump presidency, as he tries to reboot his campaign after a shaky debate performance on June 27.

"I am running and we're going to win," he said to a crowd that carried "Motown is Joetown" signs and chanted: "Don't you quit."