There's a pivotal moment that could've changed history (on this front).
In Biden's final State of the Union address, there were rumors circulating about his mental deterioration. A lot of insiders were reporting similar experiences. These were often dismissed, because they sound exactly like attacks from his opponents, particularly on the right.
Then the address happened. Biden was entirely present. He was passionate, he was articulate. He showed no signs of what people were claiming. Clearly, he had a very good day. The criticisms and reports stopped, although he skipped a number of traditional public appearances.
Fast forward a few months to the debate, and he had a bad night. Everything that people had been warning about, was on full display. To make it worse, Trump's dementia was having a good day.
What would've happened if the SOTU had happened on a bad day?