If it’s viable to run someone else, I’m pretty sure that it has to happen almost immediately, if it’s going to happen. The primaries have already happened, so if someone gets run, it’d have to be the party picking them already, and there’s very limited time to campaign.

The general election is November 5. It’s currently July 17. That’s three-and-a-half months in which someone would have to sell themselves to the public.

goes back to look at presidents who didn’t run again

https://www.britannica.com/story/have-any-us-presidents-decided-not-to-run-for-a-second-term

Johnson is not the only U.S. president who decided not to seek a second elected term. The others are James K. Polk, James Buchanan, Rutherford B. Hayes, Calvin Coolidge, and Harry S. Truman. (Theodore Roosevelt declined to run in 1908, after being elected president in 1904 and serving one term, but he again sought the office—and lost—as a third-party candidate in 1912.)

• LBJ did it prior to the primaries, at the end of March of the election year.

• Polk apparently promised in his initial campaign that he would only serve one term, so it was known long in advance.

• Buchanan promised in his inaugural speech that he would serve only one term, so it was known almost as far in advance.

• Hayes apparently also pledged not to run for re-election.

• Coolidge apparently announced the summer prior to the election year, so over a year prior to the general election.

• Truman did it at the end of March of the election year. So relatively-close, but still with seven months to go.

• Teddy Roosevelt apparently announced after being elected the first time that he would not seek a second term.

So looks like the closest equivalent would be LBJ and Truman, and they still did so at the end of March in the election year, with twice the amount of time remaining that’s still left for 2024, and before the primaries.

Like, I don’t think that it’d be realistic to wait and see what happens in the polls and then have someone run with even less time.