Laurence Tribe: is taxing AIG punitive?

Yesterday, Laurence Tribe told me that if we were to enact a narrow tax law targeting AIG, it could pass constitutional muster if (among other things) "the aim of such a tax would be manifestly regulatory and fiscal rather than punitive and condemnatory." I thought this was curious -- it certainly seems like some lawmakers are saying punitive and condemnatory things about AIG -- and asked him to clarify. He responds:

Some perception of political retribution might be unavoidable, but that's not enough to render such a measure unconstitutional. It's well established that the impassioned remarks and subjective intentions of scattered members of Congress don't suffice to condemn as a purely punitive enactment an otherwise valid regulatory or tax measure. If the law were otherwise, it would be much too easy for lawmakers to doom laws with poison-pill remarks.

I don't know how to judge the likelihood of the Tribe's hypothetical in the last sentence, but the first point Tribe makes here seems like a good one: the intention of an individual lawmaker that support a bill is not synonymous with the bill's "legislative intent." Assuming Tribe is right on the attainder doctrine (and I have every reason to believe he is) , I think I was wrong in my original post.