Leaving an ineffective president in office will undercut the Democrats. Only the president in person can vigorously advocate a policy line, and get senators and congresscritters to cooperate in his program. Without a strong central point of control, various pretenders will pull in different directions and accomplish absolutely nothing. If no legislation passes, of course the Democrats will blame the Republicans, but the voters will blame the president.
Fortunately, Kamala and Nancy are ready for duty. /S