One of the main themes in my work is how much more power Congress has than the president, and how our emphasis on the president thus distorts our view of what's possible and why the things we want to see happening aren't happening.
The most common and persuasive rejoinder to this argument is, sure, that's true on domestic policy, but on foreign policy, the president really is the key actor. There is, in practice, something to that: The president tends to have much more autonomy on foreign policy than on domestic policy. But that's only because Congress has chosen to give him that autonomy, and he has chosen to take it. Take this comment from Mitt Romney's interview with CBS's Bob Schieffer:
I can assure you if I’m president, the Iranians will have no question but that I will be willing to take military action if necessary to prevent them from becoming a nuclear threat to the world. I don’t believe at this stage, therefore, if I’m president that we need to have a war powers approval or special authorization for military force. The President has that capacity now.
I'd put it slightly differently: What Romney is saying is that he believes that if he, as president, decides to take the United States to war, Congress won't stop him. And he's probably right about that. But it's important to state what's going on clearly. This is not a power the president has under the Constitution. It's a power he has on loan from the Congress. And they could take it back if they so chose. As Drum writes, "if Congress routinely refuses to exert its own authority in the national security realm, it's Congress that's to blame when presidents arrogate too much of it. They could put a stop to it anytime they wanted."