2024 he may be different story if either Trump is extremely unpopular or an incumbent Democratic president such as Harris or Buttigieg is over 50% approval.
I think these are, more or less, the two most likely scenarios. Either a two-term president who is really unpopular drags down his party (like in 2008) or a popular one term president enters the race as a strong favorite (like in 1996). I expect we'll see at least one such election in the next five or so cycles.
I would also add that, while McCain did have a polling surge in September 2008, he was pretty consistently considered to be the underdog.
