This, from a Boston.com Q&A in December of 2007, has been making the rounds:
2. In what circumstances, if any, would the president have constitutional authority to bomb Iran without seeking a use-of-force authorization from Congress? (Specifically, what about the strategic bombing of suspected nuclear sites — a situation that does not involve stopping an IMMINENT threat?)
The President does not have power under the Constitution to unilaterally authorize a military attack in a situation that does not involve stopping an actual or imminent threat to the nation.
As Commander-in-Chief, the President does have a duty to protect and defend the United States. In instances of self-defense, the President would be within his constitutional authority to act before advising Congress or seeking its consent. History has shown us time and again, however, that military action is most successful when it is authorized and supported by the Legislative branch. It is always preferable to have the informed consent of Congress prior to any military action.
As for the specific question about bombing suspected nuclear sites, I recently introduced S.J. Res. 23, which states in part that “any offensive military action taken by the United States against Iran must be explicitly authorized by Congress.”