As the belief that Joe Biden is fully equipped to be president dissolves like mist on a Delaware morning, some of his defenders have fallen back on the idea that the American presidency is not really a man but a team. “I would take Joe Biden on his worst day at age 86 — so long as he has people around him like Avril Haines, Samantha Power, Gina Raimondo supporting him — over Donald Trump any day,” a former homeland security secretary, Jeh Johnson, said on MSNBC a few days ago. Don’t think of this as the Biden presidency, in...