President Joe Biden, in a letter to congressional Democrats, stood firm against calls for him to drop his candidacy and called for an end to the intraparty drama that has torn apart Democrats since his dismal public debate performance.

Biden’s efforts to shore up a deeply anxious Democratic Party came Monday as lawmakers returned to Washington confronting a choice: Decide whether to work to revive his campaign or try to edge out the party leader, a make-or-break time for his reelection and their own political futures.