Let’s start with the obvious. The concerns about Joe Biden are valid: He’s old. He talks slowly. He occasionally bumbles the basics in public appearances. Biden’s age is so concerning that many Biden supporters now believe he should step aside and let some other candidate become the Democratic Party’s presidential nominee. The New York Times journalist Ezra Klein made the best-available case for this view recently in a 4,000-word piece that garnered intense attention by arguing that Biden is no longer up to the task of campaign life. “He is not the campaigner he was, even five years ago,” Klein writes. “The way he moves, the energy in his voice. The Democrats denying decline are only fooling themselves.” In one sense Klein is correct. As the political strategist Mike Murphy said many moons ago, Biden’s age is like a gigantic pair of antlers he wears on his head, all day every day. Even when he does something exceptional—like visit a war zone in Ukraine, or whip inflation—the people applauding him are thinking, Can’t. Stop. Staring. …