He hasn't folded yet, the anonymous sources just say he did, you are jumping the gun. But if he does fold, then yeah, he'll look like an idiot for doing so.
Also, his approval rating being low won't matter, because the approval rating of the Democrat who runs against him will be even lower, just watch.
Trump doesn't need to be Usain Bolt to win in 2020, he just has to outrun the Democrat running against him, and he will, with ease.
Incumbent POTUS' only lose to two-term presidents, and the Democrats don't have one of those on their bench, so they are screwed.