Whether in domestic or foreign policy, Mr. Obama’s modus operandi is the same: Structure the issue as a choice between what he wants to do and an unacceptable extreme. The result, not surprisingly, is to choke off any possibility of building useful political coalitions from the outset.

With health care, the whole of GOP alternatives was “nothing new.” With Iran, it’s Mr. Obama’s deal or a “rush to war.” You get two political options: Salute or shut up.

As important as the constitutional issues raised by Mr. Obama’s unilateral authority is the political damage he has done to traditional relationships between the presidency and the institutions his methods have marginalized.

The Obama presidency has sucked the oxygen out of politics in Washington and indeed the world. But politics abhors a vacuum. The Senate letter to Iran more than anything is the system bursting outside its normal channels. Desperate Ukraine, abandoned to Russia by the U.S., has pathetically asked the U.N. to send blue-helmeted peacekeepers to eastern Ukraine.