Much of the commentary on last night’s disastrous debate has focused, quite reasonably, on the next four months and the question of whether Joe Biden can defeat Donald Trump. The answer: probably not. Yet it is critical that Donald Trump be defeated. And so there are calls—compelling calls, in my view—for Joe Biden to step aside. But let’s be honest: Last night provided ample cause for concern, not just about the next four months, but about the next four years. Even were Biden to prove the doubters wrong and and defeat Trump again, it is difficult, after last night, to...