The handwriting was on the wall. The polls were terrible, and he wasn’t getting any younger. And so, Biden decided to withdraw in the summer of 2023, and to throw his support to Harris.
You might have thought that the result would be a genuinely competitive primary and an outsider nominee, but that did not happen; Harris won over the party very quickly, and her nomination became a formality before the end of the year. Why? Because the Democrats had been united behind Biden–the left was as invested in his record as the center–so it had no viable alternative. The only possible change candidate was someone from the left, but Warren and Sanders were too old, and in any event, proposals for additional spending would have been rejected by the electorate as unrealistic and inflationary.
The bottom line with the 2024 election is that the Democrats lost it when the public decided the economy was much worse than it was during the Trump years. That happened long before Biden’s capacity became a pressing campaign issue. It is of little consolation to the left that the public was wrong, particularly if you throw 2020 into the mix, as you logically should.