“It might not be everything,” said a former administration official familiar with Iran policy. But the president’s powers “can get you a lot of the way” toward sanctions relief for Tehran.

Such a move would be audacious, and sure to enrage members of Congress. “Oh boy, the Hill will be in Defcon 1 mode,” said a Senate foreign policy aide. It could also provoke a constitutional showdown over presidential powers, sources warned, although Obama has invoked his executive authority to defy Congress on immigration and climate change…

The question of whether Obama might have a secret backup plan looms ever larger as the deal faces intense resistance on Capitol Hill, where Sen. Chuck Schumer, the presumed next Democratic Senate leader, recently announced his opposition to the deal. Congress is expected to vote on the agreement in mid-September. A rejection of the July 14 deal, followed by a veto override that even supporters of the deal say is possible, would cancel Obama’s existing authority to waive congressionally approved sanctions on Iran’s financial, energy and industrial sectors.