Hanson is an honest historian. In the past he said he was a Democrat but I don’t know if he still considers himself one. Professional historians are mostly in academia and are mostly Democrats. The most recent Presidential poll, from 2017, of 91 historians and other scholars, ranked Obama #12 among all of the Presidents—more overrated than Kennedy at #8. I wonder if the scandals will cause Obama’s ranking to drop—I would guess not, or only a little. Meanwhile, G. W. Bush was ranked #33 (lower than Carter).
That is the C-Span poll. They are talking about it on C-Span 3 right now. The Siena poll has Kennedy at 10, Obama at 17, Carter at 26, Bush at 33, and Trump at 42 (three up from the bottom). The general tendency is for Democrats to fall and Republicans to rise.
People forget how things were at the time and historians come to rely on things that are at odds with what people felt back then. Carter was at 33 in the first Siena poll when he had just left office and we had fewer presidents. Trump is better than GW Bush, but if he doesn't win reelection, he's sure to rate lower than Bush, because historians focus on procedural details that most people don't care about.