text:  Live from NPR News in Boston, I'm Steve Brown. In a letter to congressional Democrats, President Biden is standing firm against calls for him to drop his candidacy after his dismal debate performance. Biden says in the letter the question of how to move forward has been well aired over the last week, adding now it's time for it to end. Biden stresses the party has one job, which is to defeat presumptive Republican presidential nominee Donald Trump in November.