Defense Secretary Ashton Carter (L) and Chairman of the Joint Chiefs of Staff Gen. Martin Dempsey on Wednesday testified before the Senate Armed Services Committee on the Iran nuclear deal. Here they testify before the House Armed Services Committee on June 17, 2015, (Photo by Mark Wilson/Getty Images)

The military’s top brass assured senators on Wednesday that the Iran deal would not force the United States to take military options off the table to prevent the Islamic Republic from acquiring a nuclear weapon.

But if lawmakers think that means the United States can go it alone and flout the deal? Think again, administration representatives told a Senate hearing.

“The effects of a strike are temporary,” said Defense Secretary Ashton Carter, calling the Iran agreement “preferable” to any sort of military strike. “Iran would respond to an American military strike upon Iran, and one needs to think through then what the subsequent steps are, including the possibility that Iran at that point would become irreconcilably committed to getting a nuclear weapon.”

By going it alone, cabinet secretaries argued, it’s also likely the United States would wield little effective deterrent power over Iran beyond that defensive edge, beyond that military might.

“It’s at our own peril if we have a sanctions regime where we are enforcing unilateral sanctions that the rest of the world is rejecting,” said Treasury Secretary Jacob Lew, pointing out that most of Iran’s frozen assets that would come online after sanctions are lifted are in the hands of foreign banks the United States cannot control. “It’s not we go from being able to do everything to doing nothing. But what’s made the sanctions regime so effective these last few years is the fact that we’ve had the international cooperation…how do you enforce, bilaterally, countries around the world doing things against their interests just by us saying ‘we insist’?”

Lew and Carter — along with Chairman of the Joint Chiefs of Staff Gen. Martin E. Dempsey, Secretary of State John Kerry and Energy Secretary Ernest Moniz — took some of their toughest grilling on Iran from an Armed Services Committee led by one of the deal’s most vocal opponents, Sen. John McCain (R-Ariz.). McCain made a point of reminding senators that of the assembled cabinet members, only Carter and Dempsey had been invited to give their testimony on the regional security and military planning implications of the Iran deal.

Had it been just the military officials, the tenor of the hearing might have been different.

Critics of the deal have been rankled by the Obama administration’s insistence that if Congress rejects the deal, the only option is war, and they wanted to drive home the idea that the Obama administration is purposefully leaving other, independent options off the table.

Sen. Joni Ernst (R-Iowa) asked Dempsey who had advised Obama that war or the agreement were the only two options. The outgoing chairman of the Joint Chiefs of Staff said he didn’t know.

“I can tell you that we have a range of options and I always present them,” Dempsey added.

“It’s imperative that everyone on this panel understand that there are other options available out there, and a multitude of options,” Ernst said emphatically. “For the president to outright reject everything but war is outrageous to me.”

Republican senators also argued there were other non-military options the United States could take.

“The United States could go it alone, and as the secretary pointed out, we do have unilateral tools that would be effective,” said Sen. Roger Wicker (R-Miss.). “Making people choose between banking with America and banking with Iran, those tools are there.”

Kerry rejected the Republicans’ arguments.

“There’s a surreality here… the president of the United States is not mandating war. He doesn’t want to go to war, it’s not his choice, and he’s not advocating war,” he said, challenging lawmakers to tell him what their next steps would be if the United States backed away from the deal. “When you say could the United States continue some sanctions, to what end? To negotiate? I mean, with whom? You think the Ayatollah’s going to come back to negotiate?”

Lawmakers will have more time to come up with answers to those questions over the next several weeks, as they head back to their districts for the month of August. A vote on the Iran deal is expected in September.