“I think it’s a bad idea,” Paul said of quitting the accord, which the U.S. negotiated with France, Germany, Britain, China, Russia and the European Union. “This was a multilateral deal, and the reason sanctions work against Iran is because we were unified in negotiating the deal.”

Paul argued that Iran has already reaped the economic benefits of sanctions being lifted. If the U.S. were to exit, he said, it would only make it tougher for international inspectors to monitor Iran’s nuclear program.

Sen. Shelley Moore Capito (R-W.Va.) didn’t support the agreement when the Obama administration negotiated it but worries about the fallout from the U.S. going back on its word.

“I do think there’s merit to being part of a group that’s heavily monitoring what’s going on and seeing certain developments,” she said. “And I think we have to pay close attention to what our allies are saying.