Let us finish the job, said Joe Biden in his re-election video. The rest of us, including Biden, could have been forgiven for thinking he had already done that by defeating Donald Trump in 2020. Yet here we are again: two bald men fighting over a comb, as Jorge Luis Borges depicted the British-Argentine war over the Falklands. America is no comb and Trump has plenty of hair. Nor is he certain to be the Republican nominee. But a repeat battle between ageing men would test America’s tolerance.

Many rashly assume that Biden can easily beat Trump. Nothing could be more certain in Biden’s mind. With some reason, he believes that had he, rather than Hillary Clinton, had been the Democratic nominee in 2016, Trump would never have become president. Those 77,000 votes that were Trump’s winning margin in a handful of mid-western states that tipped him over the electoral college line, included Biden’s native Pennsylvania. In 2020, of course, Biden was the only candidate to defeat Trump in an election.

Thinking history will repeat itself would be a dangerous mistake. Those around Biden have made it clear that his decision to run for re-election would have been far tougher had the likely nominee been anyone other than Trump. The latter is 76, not that far below Biden’s 80 (although the gap often seems wider). As a result, Democrats have been almost willing Trump to become the Republican nominee. That now looks probable.