Key Democrats are so far withholding support for the White House’s Iran deal, worried that the plan would undermine national security, threaten Israel and too easily let Tehran escape punishing economic sanctions. Many of them will be in office beyond the end of Obama’s term, so an affirmative vote means they will effectively own the deal when they face voters again. That means they could pay a dear price politically if the accord fails to curb Iran’s nuclear ambitions and proves to be a failure.

Even members of Senate Democratic leadership, like Chuck Schumer and Jon Tester, were explicitly noncommittal, a sign of the challenges ahead for the president.

“Verification, verification, verification, verification,” said Tester (D-Mont.). “That’s the big thing. Look, I don’t trust these guys, I want to make sure that whatever we’ve agreed to, we’ve got verification that’s going to happen.”

Could he vote against the deal if those concerns aren’t satisfied?

“Oh sure,” Tester said.