According to Donald Trump, Joe Biden is either a very accomplished or utterly incompetent debater. When details of the presidential debate, which takes place in Atlanta on Thursday, were announced last month, Trump mocked Biden as “the WORST debater I have ever faced”, adding: “He can’t put two sentences together.” And yet, while speaking to the All-In podcast last week, Trump commended Biden’s showing in the 2012 vice-presidential debate. “He destroyed Paul Ryan,” Trump said. “So I’m not underestimating him.” The flip-flop could be Trump’s belated effort to temper expectations of how he will perform against an incumbent president with...