I also only partially agree with his characterization of past Presidents.
Bush Jr. has been labeled as slow, or dumb, but I tend to see him as less motivated than many others.
Clinton had/has a strong mind, maybe not brilliant but very intelligent, but as we know he sometimes let himself be easily distracted.
Others, like Bush Sr. or Reagan were, to me, so plainly wrong about so much that I tend to discount them out of hand.
But the main one who came to mind while watching this video is Obama. And yes, I am biased because of my work on his first campaign where I ran one of the local offices and went to rallies and did lots of phone work and much of the other stuff that campaign workers do. Having said all of that and then setting it aside and trying to look at Obama without any filters, like my Rose Colored glasses, I believe we are seeing one of the most learned and intelligent Presidents we have had, ever.
You're right about how the office can weigh on someone... Obama surely changed dramatically over his tenure.
It was a bit of a disappointment when he pretty much lumped all past Presidents into the same basket.
BTW... that campaign was a lot of work and loads of fun, I loved ever minute of it.