It's not fine for the perpetrator to joke about them.

I'll take a slightly different tack on this. I think it's not funny for the perpetrator to joke about them. I don't think I'm ready to debate the point of whether it was fine to make the joke. I like to believe that a joke is a joke, and one shouldn't try to read anything into it, but an example like that makes me question that point of view.

But just for a moment, let's play devil's advocate and say that Bush Honestly Thought Saddam Was Building Nukes And Wasn't Lying When He Said So. In that case, the joke is merely unfunny rather than in exceptionally poor taste. And, actually, if you think about it, that joke might help reinforce his position, if in fact that's his position (still?).