Eisenhower was the last Republican president not to be subject to rage unto paranoia, press hostility, and continual assault, disrespect, and contempt from the political opposition. (However, it is a fact that the leader of the war that saved the "free world" from fascism was widely viewed as a dunce by the Adlai Stevenson supporters.)
If you are old enough to recall, Nixon was subject to what we would now call a "Nixon Derangement Syndrome" which finally brought him down. So were Ford and Reagan and Bush 41. All were demonized, called "stupid," and intensely hated by the opposition.
Having learned this unfortunate lesson, the Republicans finally decided to try that same game with Clinton, who they managed to handcuff politically via relentless ankle-biting, but were never able to rally intense hatred against him - probably partly because of press sympathy but also because the foundations of hatred were not present.
Where does this hatred come from? I think the Left believes that they are the "good smart guys," and any Repub a "bad dumb guy." I do not think that Conservatives tend to use such a black-and-white view of politics. Most Conservatives I know do not see themselves as the good guys, but as having better ideas. Thus, amongst Liberals, you rarely see the kind of social stresses that people like neo-neocon go through in being a neocon in a Left-liberal community.
(Take me, for an example. I do not believe that I am "smarter" or "better" than Leftys and Liberals. I do believe that the ideas I hold about the relationship of the individual to the State are better ideas, that offer to bring out the best in people, but "some of my best friends are liberals," and it doesn't bother me at all. Friendship and shared interests should trump politics. When my Liberal pals are willing to discuss issues rationally, and not emotionally, I think it can be fun to debate and that it can add something to a friendship.)
Along with the good guy/bad guy syndrome comes a sense of entitlement, I believe. If we are the good guys, then we deserve to be in charge. If we aren't, then something has gone terribly wrong, or something nefarious has occurred, or Americans are idiots. Feeling powerless when you "know" you are right makes some people nuts. (Never forget, though, that if American voters are idiots - it's the same idiots that vote when you win an election.)
I find the hatred that is generated by this disappointed sense of entitlement to be very destructive. Debating ideas and world views is great, but hatred, lying, tantrums, and attribution of malevolence to other public servants is not the civil society I want to live in.
(I also believe that not everything about this subject is psychological, per se. Liberals care more intensely about politics, because they are more invested in the role and power of the state. As a rule of thumb, except in the case of war, Conservatives tend to want to lessen the power of the State over the individual, Liberals to increase it. And yes, I think Bush is a conservative at heart, but a politician in practice....and I mean in "practice".)
My message to the Bush-Deranged: there is no good vs. bad here. There are simply differing ideas and differing views of human nature - all deserving of rational debate. Let's debate - not hate.