I feel a certain call to speak out on this, as a person at least titularly involved in the creation and delivery of jokes. If you say something to me, and I look hurt, and you say, “Just kidding,” that does not make what you said a joke. It has to be a joke in the first place. And Kerry’s line is very clearly, both in its wording and in its delivery, not a joke. It’s a warning. He’s talking to students. He says it with an even graver-than-usual, flatter-than-usual tone, and he’s telling them what can happen to them if they don’t study hard. Is he warning them that they might someday be President and make decisions leading to a quagmire in Iraq? Of course not. You can get stuck in Iraq. Personally.
Beyond that, if the line were, as claimed, a joke about the President, it would theoretically need to contain at least some tiny reference to the President. I could rewrite it a dozen ways to make it a joke, though never a good one — “You can stay in school and study hard and do well, or you can coast through school like our President and end up stuck in Iraq.” But that’s not even close to what Kerry said.
Also, I think those who defend the idea that he meant the President are misreading the line “you get stuck in Iraq.” It’s a subtle matter of inflection, but I don’t believe he is saying “stuck” in the sense of “mired.” I believe he is saying “stuck” as “unfortunately placed” as in “I got stuck in the worst hotel room.” Again, the President could not be placed in Iraq. Soldiers can.