In Book Excerpt, Kamala Harris Says Leaving Reelection Decision to Biden Was “Recklessness”

Since the advent of the modern primary election system in 1972, an incumbent president has never been defeated by a primary challenger, though every president who faced a strong primary challenge went on to be defeated in the general election.

https://en.wikipedia.org/wiki/Primary_challenge

Which is exactly why everyone said it was Biden's decision. A strong primary challenger meant Biden would lose. Should Biden have been convinced to not seek re-election sooner? Yes. But that's still his decision.

The time for Biden to step aside would have been right after the midterms. Maybe behind the scenes Harris tried to convince Biden, but she clearly failed. Maybe Biden really was at the top of his game and no one saw it until his debate performance, but I'm not sure anyone really believes that. Publicly Team Biden said he was doing backflips around the White House, but of course when the public saw him he was your typical old man.

So... whos to blame? I blame the Democratic party/DNC at large. It's clear to me most people who vote Democrat want someone more progressive. The DNC would rather play it safe.