Donald Trump has long attacked Joe Biden, his likely opponent at the polls next year, as “Sleepy Joe”, portraying the 80-year-old president as too old and too mentally fogged to occupy the Oval Office. As recently as Friday, the former president attacked his successor for being unfit to deal with Russia and the threat of nuclear war. But Trump’s tactics rebounded when he said Biden threatened to lead the US into “world war two” – and suggested that he, Trump, thought he had beaten Barack Obama for the presidency back in 2016. There have been two world wars. The first...