The seeds of President Joe Biden’s reaction to the Democratic Party’s crisis of confidence in him were planted years ago. Facing an extraordinary push by his friends and allies to end his political career, Biden has responded with defiance. For three weeks, he has dug in, denied polling evidence and vowed to stay in the race, claiming that he is the only one who can defeat former President Donald Trump. Only in the last few days have people close to him said they believe he is more receptive to stepping down. To many of his allies, he is in a...