When asked during an October 2016 debate about whether he would abide by the voters’ will, Trump responded that he would “keep you in suspense”. It is unlikely that any chaos in states with universal mail-in voting will cause the election result to be inaccurately tabulated, as Trump has suggested.

The five states that already have such balloting have had time to ramp up their systems, while four states newly adopting it — California, New Jersey, Nevada and Vermont — have not. Washington, DC, is also newly adopting it.

Of those nine states, only Nevada is a battleground, worth six electoral votes and likely to be pivotal only in a national presidential deadlock.

California, New Jersey, Vermont and DC are overwhelmingly Democratic and likely to be won by that party’s nominee, former vice president Joe Biden.