There was an undercurrent of fear at last week’s Democratic convention. But the anxiety gnawing at the party was not focused on worries that Republican incumbent Donald Trump would actually win the US presidential election. It was that the president would steal it — by sabotaging the vote or refusing to concede defeat. The comedian, Sarah Cooper, summed up the prevailing view when she said “Donald Trump knows he can’t win fair and square.”

The president has, after all, refused to commit to accepting the results of the election. But, by focusing on the danger of a stolen vote, the Democrats are in danger of underplaying a more conventional risk — that Mr Trump could win without cheating. 

It is true that polls show Joe Biden, the Democratic nominee, well ahead of Mr Trump and have done for months. Those who point out that the polls also predicted victory for Hillary Clinton in 2016 are reminded that Mr Biden’s current average lead of around 9 percentage points is much larger than that held by Mrs Clinton.