I think there are two scenarios.
1. Utilize and extend the meaning of current Congressional mandates
2. Conduct a PR campaign aimed at justifying attacking Iran. When the numbers are right it should force Congress to pass the "right" bills to authorize the administration to attack Iran.
This is the same situation the administration was in in 2002 when Powell suggested going to the UN. The administration had already made up it's mind to invade Iraq (which would be the fall back position) but a UN resolution would legalize an invasion so it was worth waiting for. The propaganda campaign mounted by the administration worked and forced Congress to authorize use of force. The UN didn't pass a use of military force resolution so the administration got one of their brilliant attorneys to stretch the meaning of UN 1441.
It becomes more compelling when viewed from the administrations rebuttals that everyone is complicit i.e. the American people were overwhelmingly in favor and Congress overwhelmingly authorized use of force, therefore everyone is to blame not just the administration. Of course the contingency plan bomb 'em anyway, is always a go.
