President Obama has been criticized by me and others for proceeding as if he has the legal authority to authorize acts of war against Syria, even though he declared in writing as a U.S. senator, "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."
It turns out that his Democratic primary opponent and eventual running mate, then-Senator Joe Biden, had even stronger views about presidents attacking other nations without Congress's permission:
Chris Matthews: You said that if the United States had launched at attack on Iran without Congressional approval, that would've been an impeachable offense. Do you want to review that comment you made?
Joe Biden: Absolutely. I want to stand by that comment I made. The reason I made the comment was as a warning. I don't say those things lightly, Chris. you've known me for a long time. I was Chairman of the Judiciary Committee for 17 years. I teach separation of powers in Constitutional law. This is something I know. So I brought a group of Constitutional scholars together to write a piece that I'm going to deliver to the whole United States Senate pointing out that the president HAS NO CONSTITUTIONAL AUTHORITY to take this country to war against a country of 70 million people unless we're attacked or unless there is proof that we are about to be attacked. And if he does, I would move to impeach him. The House obviously has to do that, but I would lead an effort to impeach him. The reason for my doing that -- and I don't say it lightly, I don't say it lightly.
This is a striking statement.