FROM MEMORY - the very latest I know of that a President chose not to run, is Johnson, in '68. Most of the other one-termers either declared ahead of time they weren't running - OR - (ironically, LIKE Biden did) - run on the promise it would be just one term.
Six Presidents made it clear they didn't want to run again - Polk, Buchanan, Hayes, Coolidge, Truman and Johnson were eligible but chose not to. Polk campaigned on being a one-term. Buchanan was a TERRIBLE President, and would almost certainly not have even got the nomination. Hayes said he would only serve one term. Hoover was simply disastrous and could see the writing on the wall. Coolidge SAID "I do not choose to run" but insiders said he hoped they would draft him anyway.
Coolidge made his statement not to run in August 2, 1927 - the year BEFORE the election.
Truman announced, late in March of 1952 - his approval rating was around 22 percent.
Hayes, Polk and Buchanan were never in contention - they never even bothered.
Johnson saw the writing on the wall - unpopular war, unpopular President - and a rising star named Bobby Kennedy. He left in March of '68.
No, to my knowledge, what is going on with Biden is utterly unprecedented, and it is ENTIRELY based on bad polling that happened after his dreadful debate - where the cat was finally out of the bag - he's an old, doddering, senile man. HAD THAT NOT HAPPENED - they would still be on board with him. This is not about "democracy". They are already concocting excuses about how the primaries aren't voted on by many voters and they really didn't have any choices anyway. No, this is naked grab for power.