Joe Scarborough, the former congressman, ally of President Biden and influential host of the MSNBC show “Morning Joe,” on Thursday morning all but called on Mr. Biden’s aides to help him exit the race. Mr. Scarborough has been blunt that the president’s debate performance against former President Donald J. Trump on June 27 was calamitous but has also interviewed Mr. Biden since and was sympathetic to him in the days following the debate. On Thursday, the host cited polling for the president...