Odd.
The U.S. has banned import of Iranian oil since 1995, when Clinton signed Executive Order #12959, which was renewed by George W. in March of 2004.
A much more likely attack scenario would be Iran accumulating enough fissionables from their emerging nuclear weapons program to support at least one device. We'd have to play referee in that event (again), because the attack wouldn't be led by the Americans. It would be an act of Israeli "pre-emptive self-defense".
Israel would be at the pointy end of the stick as soon as Mossad/CIA got the word that the Iranians were close to their goal, in a scene eerily reminiscent of Israel's previous attack on the Iraqi reactor at Osirak. Some think it'll happen sooner rather than later, because they've already asked the U.S. to provide CSAR support in the region for the Israeli Air Force - which we quickly and quietly declined.