Writes Walter Shapiro, in The New Republic.

If Biden dropped out at any point before the Democratic convention, it is virtually certain there would be a contested battle for the nomination…. and not even a Biden endorsement of Kamala Harris would change that…. Maybe things might be different if Harris were universally beloved in the party and had an unequivocal edge on Donald Trump in the polls…. 
If Biden announced on the Monday after Thanksgiving that he would be retiring, it would give 2024 presidential contenders fewer than 100 days to declare their candidacies and define their image before 14 states pick delegates on Super Tuesday, March 5…. Even a globe-trotting governor like Newsom… would be ill prepared for the full range of queries that would be immediately hurled at him as a presidential candidate….  
[A] replacement candidate forced to plunge into the middle of a campaign without a rehearsal period may appear to the voters as a more flawed option than Biden does today.

By my reckoning, Biden made a heedless mistake by not bowing out of the 2024 presidential race last spring, knowing that his age would be a political liability…. And at this point, Biden—despite his obvious flaws as a candidate—is probably the Democrats’ best option for president against Trump….

Shapiro makes a lot of points but there’s one he won’t even consider: Trump defeated Biden. Everything was thrown at Trump, and he’s still on top, stronger than ever. Trump was supposed to defeat himself, leaving Biden free to continue walking — stumbling — forward in the Presidency that was already his. But it turned out Biden needed to fight for reelection. 

If the real point here is Trump’s outstanding — and mystifying! — strength, then Biden’s stepping out of the way won’t help. It’s not just that “a replacement candidate [is] forced to plunge into the middle of a campaign without a rehearsal” — it’s that a replacement candidate is forced to go up — suddenly and without preparation — against Trump