Progressives and Congressional Black Caucus members are among the loudest voices defending the president

Democrats on Capitol Hill have thus far largely fallen in line behind President Biden or stopped short of calling for him to withdraw from the race, as he continues to try to assure Democratic voters and donors that he can effectively campaign against, and ultimately defeat, Donald Trump.

His backers point to his legislative record, saying it is deserving of a second term and that they can campaign on achievements such as the infrastructure law and a measure that lowered prescription drug prices. Others say it would be unfair to call for him to...