He's giving Reagan a run for his money on two fronts: as a bad actor and as an Alzheimer's victim.
Bush made terrible decisions but he was in no way dumb(atleast not as dumb as Trump)
Here read this -
George W. Bush wasn’t dumb, but he was still a bad president - Washington Post
What about Harding? Although Trump’s scandals are like watergate and teapot dome all rolled into one.