People didn't underestimate Bush. They overestimated the Right. And have continued to do so lo these many years.
There aren't a bunch of Impeach Trump signs because the Left has come to realize that the Right are totally 100% down with a world in which black men get shot by cops, in which white kids get a pass for raping white women, and in which brown children are taken away from brown parents. With GWB, we thought they could be made to see reason. With Trump, we're afraid to see how insane they truly are.