Donald Trump has a conundrum. Despite some hemming and hawing, he made the right call in debating President Joe Biden and won the battle of “who looks oldest.” He certainly can’t reprise that against Vice President Kamala Harris at the ABC News debate on Sept. 10. And the optics of “prosecutor vs. felon” are brutal for Trump. Unlike Biden, Harris won’t bizarrely let that go. Trump also doesn’t want to talk about abortion, which Harris will hit hard. He will surely rail against immigration, but...