This isn't a hypothetical problem. Trump is dead politically, but the dissatisfaction that made his brand of populism electable is still there.
And if Biden - or Harris - don't take steps to address it by 2024, someone much worse than Trump will appear.
And they may well win.
The reality is voters on both sides vote how the various media outlets tell them to vote. There's plenty of media noise, but the available narratives are carefully curated, and voters don't get to generate their own from the grassroots upwards.
This has become far more dangerous as Facebook and the various other online platforms have moved towards microprofiling and microtargetting.
This was a huge issue during the Brexit campaign, when disingenuous single-issue ads aimed at very narrow demographics with specific vulnerabilities put the result over the top.
Trump spent more on social in this election than Biden did, and the result was a good collection of surprise wins in states like Florida, and the second biggest voter turnout in US history.
If Trump had been even slightly more competent and focused and if Covid hadn't been happening this would have been a bloodbath for progressives.