Bush’s success suggests that, one way or another, Obama will also prevail in implementing the Iran deal. He either will beat back a congressional attempt to strip him of sanctions power, or if not, likely will secure enough Hill votes to sustain a veto. But his options do not end there. Presidents as commanders in chief have enormous power when dealing with national security issues, if — as Obama and Bush both do and did — they deeply believe in what they are doing. Even if Congress strips him of the power to lift sanctions, the president could dither on implementing them, or deploy his authority in what he keeps asserting is a “war or peace” situation to ignore Congress. Finally, he could cut a side deal to trade limited American noncompliance with the deal (i.e., some U.S. sanctions remain) for commensurate Iranian noncompliance, for example on verification terms, centrifuge numbers or stockpile limits.

But aside from presidential grit and creative legal reasoning, there is another reason that Obama is likely to prevail. The international system over which the United States still presides rests on the ability of the American president to act unilaterally even on unpopular decisions if a vital national interest is at stake. Bush, facing the collapse of his Iraq policy if he could not curb that country’s descent into civil war, acted on such an interest, despite resistance in Congress, deep skepticism in the Iraq Study Group and doubts among many top advisers.

We see similar behavior by Obama on Iran.