I think the leftists have put themselves into a little PC box, and that's why the "joke" makes sense to them. What other example can a democrat use as a symbol of failure? The homeless? Single mothers? Factory workers? There aren't many groups the left can safely mock......

Even if Kerry was trying to make a joke about Bush's intellect, the force of the joke only works if the Senator believes his target audience understands that:

"Bush is stupid;"

"It's stupid to be in Iraq;"

"Bush is in Iraq, which shows he's stupid."

Points "A" and "C" only work as a joke if both Kerry and the students in audience believe point "B" is true. And that's the problem -- Kerry can apologize/explain all he wants, but the only way the failed joke makes a whit of sense is if you believe the premise that anyone getting involved in Iraq isn't as smart as you are. If you say you don't mean U.S. troops are in Iraq because they're stupid, or that you have to be stupid to be stuck in Iraq then where's the humor in saying Bush is stupid/Bush is in Iraq?

The things on the Leftists "Safe To Hate" list is actually quite long, and all of them are mockable (some examples):

"Christers" of any variety
Mormons
McDonalds
"Gun Nuts"
Smokers
Walmart
Any private vehicle larger than your own
Snowmobiles

And when you make a joke about someone being "stupid", it helps to not keep repeatedly demonstrating that you aren't any smarter.

As I've stated, John Kerry is an idiot.

I thought Gore was stupid, but Kerry plumbs new depths.

I don't care if Diebold rigged every voting machine in OH, I thank God everyday that this idiot isn't our president.

It doesn't work to tell a joke that suggests that someone is stupid if has been demonstrated by SAT scores and military intelligence tests that the person telling the joke is the one of the two who is less intelligent.