Joe Biden’s age is written on his resting face, the one that stares into camera like it’s your fault.

It’s the look of his 81 years and it doesn’t look great on a debate stage – more ready for bed than for a second term.

It matters in Atlanta.

Biden enters the TV face-off ridiculed by opponents as mentally unfit for the job.

It’s a perception embedded in the public consciousness, fed by high-profile episodes of supposed “brain freeze” – this, despite a robust rejection of frailty by the White House.

A CBS/YouGov poll earlier this month found that only about a third of voters thought Biden had the cognitive ability to serve as president, compared with half for Trump.

How Biden performs in the hostile environment of a no-notes, live TV debate could be an occasion to confirm or confound age concern.

He needs to avoid reinforcing the notion of weakness.

If this occasion is pivotal in the presidential race, that’s where the pivot point lies.

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Biden freezes during holiday celebrations

Millions will watch the debate from start to finish but millions won’t – they’ll consume it via the social media breakdown and base their judgements accordingly.

Ninety minutes of television will come down, largely, to viral “moments”, cut and pasted as campaign touchstones to drive fundraising and political ads.

In the modern era, they are the moments that can define a political campaign and the difference between success and failure – a TV contest, and so more, could be lost on a momentary lapse.

Biden ‘shadow-boxing’ ahead of main event

The president and his team have been shadow-boxing through mock debates at his Camp David retreat. Biden’s personal lawyer, Bob Bauer has been playing the role of Trump.

Faking it in the Maryland hills will be in stark contrast to the real thing in Atlanta.

Presidential advisers who micro-manage their man and his environment will be throwing him solo into a situation uncontrolled and unpredictable.

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They will settle for “State of the Union” Biden. In addressing America’s political establishment in March, his performance was suitably presidential.

As Democrats sighed relief, Trump growled resentment, accusing Biden of being “all jacked up” on cocaine.

He’s at it again, suggesting that the president will take a “shot in the ass” as a chemical booster ahead of the TV debate – in doing so, he’s laying the ground for a strong Biden performance, having previously written him off.

Trump’s less structured preparations

Donald Trump’s preparations have been less structured than Biden’s. Advisers have told him to focus on subject matter with which he scores best with voters – inflation, immigration and crime among them.

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How did Biden beat Trump in the 2020 debates?

The two men haven’t been in the same room together since they last debated before the 2020 election.

Four years on, the conditions are different. There will be no studio audience for punchline response and reassurance, only a penetrating silence that will sharpen scrutiny – from the moderators and from each other.

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Trump supporters suggest he’ll benefit from the absence of an audience because a calming effect will rein in his instinct towards belligerence.

His detractors counter that a Trump performance is built on crowd interaction and he’ll struggle in a sterile setting that requires rounded argument.

We’ll find out when the two old foes enter the stage, presumably with a handshake although that’s not been confirmed.

If the choreography allows, it will be the coldest greeting ahead of a hotly anticipated night.