Newsom wants it too, I think, and any discussion that cuts out Kamala, well, I can think of at least one person who's gonna take issue with that. And potentially many other Black Americans.

It is too late to mount a serious campaign, though. Swapping out Joe for another candidate undermines the legitimacy of future primaries, and it's already been reported that the Heritage Foundation (project 2025 authors) is looking into using a late election cycle candidate swap to bolster any potential election suits should Trump lose. And I've yet to see a convincing poll-tested analysis that shows another candidate being able to take on Trump. Yes, the "generic dem" polls better, but as soon as you slap a name on it, the favorability drops by something like 20%, is my current understanding.

edit: here is polling from yesterday

It isn't some sort of pro-Biden hysteria driving my concerns here, I want to assure everyone. I'm not terribly fond of him. The only thing that matters is beating Donald Trump, and I think Biden's still the best shot we have. It's unfortunate.

For posterity: 1930s Germany also didn't take Hitler at his word, either, btw. They thought it was rhetorical bombast, that he was an un-serious, comical figure.