My recollection is that a reporter cited an anonymous source who was thought to be a member of Biden's campaign staff. The staffer claimed that Biden had privately stated that he would not run for reelection unless he thought himself healthy enough to run again.
Out flawless 3rd estate quickly turned that into "If elected, Biden promised to only serve one term!"
Now if he does run again they'll claim he's breaking a promise.![]()
To paraphrase an old joke, Biden doesn't have to be extremely popular. Just more popular than the other guy.