By being such a complete travesty of what a president is supposed to be, he forces many centrists and principled conservatives to hold their nose and vote for Biden along with the moderate left and the far left. Biden's supporters are spread across most of the political spectrum - so if he gets elected, then whatever path he takes, he's certain to greatly annoy a good deal of the people who voted for him. Many of them are already aware of that, but I guess there will still be plenty who will be surprised and angry about it.

Though even without such Republicans/independents disgusted by Trump, the current Democratic party itself covers an uncomfortably wide range of positions. In a country with a more balanced electoral system, Biden would have been in a different party altogether from Sanders, Ocasio-Cortez and their supporters, perhaps together with moderate Republicans.