They should have learned that after Obama won the first time. Bush winning reelection showed most Democrats that anything could happen no matter how terrible the other candidate was.
as bad as things were four years ago, they're worse now. the tea party didn't exist as an entity, and the country is more divided in general on where to go. the people who didn't like the black guy who needed a teevee to talk gud now hate him for ruining the country. they've made gains in congress and believe the momentum is on their side, and more: think that everyone hates the president as much as they do.
there's also the matter of god- who i'm sure many of the most fervent anti-obama people have been praying to to have the guy removed from office. some republicans are going to have physically violent reactions. i'm sure some democrats did in 2004, but now we have youtube. so that'll be neat.