By mocking Biden, and suggesting he’ll need performance-enhancing drugs to make it through 90 minutes, Trump has usefully lowered expectations for his opponent. But the 81-year-old president cannot simply run down the clock in the hope of avoiding a gaffe, a brain fade or an election-losing freeze. Biden needs to summon the same energy he exhibited in delivering his annual State of the Union address in March, a bravura performance in which he mounted a vigorous defence of his presidency.

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Biden, after all, has a positive story to impart. Inflation has fallen to 3.27 per cent, a long way down from its 2022 peak of over 9 per cent. The trade deficit with China is at its lowest level in 14 years. True, the “felt economy” for millions of Americans is nowhere near as strong as the real thing. A recent poll suggested more than half of voters believe the US economy is in recession. But in tandem with the Federal Reserve, “Bidenomics” has tamed inflation without a dramatic spike in joblessness.

Television, of course, is an impressionistic medium, and televised debates linger in the memory not for the power of the messaging but rather for their memeable moments. The zingers, the gaffes and fiery exchanges which are run, ad nauseam, thereafter. The glaze of flop sweat that made Richard Nixon look so shifty was seen as a turning point in the 1960 campaign.

Ludicrous though it seems, when Biden and Trump come face to face in the first-ever debate between a sitting and former president, the future of US democracy could turn on one such split-second flashpoint. So we are in for an anxious watch. Not so much pass the popcorn, as pass the sick bag.

Nick Bryant, a former BBC Washington correspondent, is the author of The Forever War: American’s Unending Conflict with Itself.