You know, it's worth remembering that when the Bush administration wanted to invade Iraq, they spent the better part of two years pursuing a massive PR strategy to sell the deployment. Going to war is actually a relatively tough thing to do, even in a system that gives fairly significant levels of foreign policy autonomy to the executive.
But when talking about going to war with Iran, a lot of arguments rest on what I'll call the reverse-crazy theory. It's become a truism among liberals that you can't rule out any Bush administration actions based on the formerly useful analytical strategy of "doing that would be $^%&# nuts." Some folks, though, take that a bit further, and come pretty close to saying that the Bush administration will do X because X is $^%&# nuts, and so are they. But I don't buy that.