The only silver lining to Biden’s painful performance? US voters had already made up their minds | Emma Brockes

Who could have foreseen that the scariest thing about the presidential debate on Thursday night wouldn’t be the lies, the bombast or the threats to democracy, but the spectacle of Trump’s slightly wolfish restraint. Heading into the encounter, Democrats felt the kind of anxiety more usually endured before watching a child perform, with that same crushing sense of raw emotions. That Trump barely mocked Biden, or went after his age or his son, seemed less rehearsed than a shrewd response to what all of us were seeing: a president so compromised that all Trump had to do was grin, lean back and let the optics work for him.

And still, despite the evidence, it feels wanton to say this. Biden, whose voice was hoarse from a cold, rushed his delivery, fought to find words and stumbled in a style not entirely new to him. The difference on Thursday night was one of degree. “Oh my God” was the general consensus, texted around the country, when the debate opened in Atlanta. While Trump’s remarks were predictably ludicrous, full of lies and inflated claims , nothing he said could distract from the image of Biden saying sensible things in a manner so crepuscular that the entire event jumped from politics to tragedy. It made me think of a line from Rilke: “It had almost hurt to see.”

This was the near-universal response among Democrats on Friday morning. Spoken with slightly too much relish and accompanied by a lot of “we’re doomed” hand-waving, it drew attention once again to everything that’s wrong with political discourse. There was Trump, claiming, crazily, that in Democratic states something he called “abortion after birth” was endorsed, while Biden soberly listed his achievements in job creation, managing inflation and proposals to better tax those paid more than $400,000. The president pushed back against Trump’s lies as best he could, unaided by the two CNN moderators who, scandalously, were far more corpse-like in their affect than the president. It didn’t matter. The gut response of everyone watching was not “here are two men, one vastly superior to the other”. It was simple shock at how Biden has aged.

There was anger here, too. A point widely made on social media on Thursday night was that this is what a race for the most powerful job in the world looks like when people won’t vote for a woman. Two elderly men, in various states of impairment, addressing each other as “this guy”, squabbling over who has the better golf handicap and accusing each other of being sore losers. It was like one of those bad 90s satires involving Warren Beatty, in which the joke is too broad to land. Trump thinned his lips, repeated the phrase “kill the baby”, and accused Biden of running the worst administration in history, to which Biden, correctly but uselessly, in effect responded “no, you are”.

And still there was worse to come. For me, the hardest parts of the 90 minutes were the brief flashes of Biden as he once was, full of easy charm and conviction. It was clear that the president was operating in a mode less professional than personal; that his unfiltered state was, on occasion, less strategic than the result of some other, inhibition-suppressing dynamic. But in those moments of pure, visceral response to Trump’s awfulness, Biden seemed like a stand-in for all of us.

Related: Biden struggles to land lines as Trump lies in first presidential debate

Several times, one saw Biden look across at Trump with pure, unmoderated hatred. “He didn’t do a damn thing,” he said in reference to Trump and 6 January ^. “Such a whiner, he is,” said Biden, the odd syntax removing the remarks from the context of a presidential debate to what felt like an honest and off-camera response. “Something snapped in you when you lost,” he said and it was an extraordinary moment, watching a man present Trump with a flat truth about himself. When Biden cracked a huge smile in response to the audaciousness of yet another Trump lie, the pathos was almost unbearable. There he was, fully himself for a moment, the man we recognise as a capable and charismatic leader.

Trump, in these moments of confrontation, pursed his lips and smiled thinly. You could almost see the machinery of his personality working, the split-second flare of his wounded narcissism, followed immediately by denial and attack. By the end of the debate, while Democrats started talking, pointlessly, about replacing Biden on the ticket , the only consolation was in the broken political system itself. These debates don’t move the needle. They exist in the absence of any better ideas on how to engage the electorate. Americans are so polarised that no one is changing their minds. If Biden’s performance was terrible, one could self-soothe with the observation that it hardly matters at this stage; which is, of course, the most terrifying conclusion of all.

• Emma Brockes is a Guardian columnist