[Candidate Obama] responded in writing to a series of questions regarding executive power from Charlie Savage, then of The Boston Globe:
Q. 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?)
OBAMA: 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.
Biden in 2007 on the possibility of Bush using force against Iran:
“The president has no constitutional authority to take this country to war… unless we’re attacked or unless there is proof that we are about to be attacked,” Biden said.
"The Founding Fathers were, as in most things, profoundly right. That’s why I want to be very clear: if the President takes us to war with Iran without Congressional approval, I will call for his impeachment."
"I do not say this lightly or to be provocative. I am dead serious. I have chaired the Senate Judiciary Committee. I still teach constitutional law. I’ve consulted with some of our leading constitutional scholars. The Constitution is clear. And so am I."
"I’m saying this now to put the administration on notice and hopefully to deter the President from taking unilateral action in the last year of his administration. If war is warranted with a nation of 70 million people, it warrants coming to Congress and the American people first."