We could still avoid Orange Hitler if one of them dies or is otherwise eliminated from the election, such as by conviction for a coup attempt. But presuming both stay in it, there are still things Biden could do.
An ad campaign simply playing Trump's own Hitleresque words would help. Not just saying he's like that; Democrats have been saying that about all Republicans at least since 1990 and people are used to the fact that it's always been lies before now. Also no "Let's be positive & hopeful" crap because nobody's buying it anymore. When there's only one thing you're really offering and one possible reason to vote for you, that one thing (not being Orange Hitler) needs to be what you keep reminding people of.
But more important than any ad campaign would be just doing his current job better. He was more popular when he was doing things people liked or even just putting in a token act of even feebly sort-of trying. But he hasn't done much of anything for a while, at least not things people like. His sinking popularity at the same time has not been a coincidence.
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