Joe Biden is old. Like each of us, he comes from a particular place in history, in his case the LBJ years. And that’s one big reason why his first term has been so full of accomplishment: His age, often cited as the greatest obstacle to his reelection, is actually his superpower. The first presidential election in which Joe Biden was eligible to vote featured Lyndon Johnson beating Barry Goldwater. History remembers LBJ’s presidency as chaotic because of his tragic adventuring in Vietnam, but in other respects it was remarkable. His Great Society echoed Franklin Roosevelt’s New Deal (FDR was...