The Iran deal is a done deal. President Barack Obama has enough Senate votes to ensure that it ultimately goes through.

Sure, the deal has flaws and could have been tighter. But GOP candidates and legislators who have whipped up hysteria on Capitol Hill have never offered a plausible alternative. Nor have they been honest about the negative consequences if this deal were thwarted. (And of course they’ve never admitted that George W. Bush’sIraq war paved the way for Tehran’s power surge in Iraq, Syria and the Gulf.)

With the deal assured, there’s an urgent need for serious debate in Congress over how to curb aggressive Iranian behavior once sanctions are lifted. Instead, we’re likely to see more Trumped up political theater rather than efforts to bolster the accord.

“It is a problem for the agreement and for what you do next if you don’t have consensus in the legislature,” says Sen. Robert Casey Jr., D-Pa., who provided one of the final votes that gave Obama a veto-proof margin. In a phone interview, the senator explained why he decided to support the deal, and what Congress should do to help make it work.

“This was one of the most difficult decisions of my public career,” says Casey. He spent extensive time poring over the accord, and talking with experts and top administration officials, including the president. “I don’t remember an issue in all my years in the Senate where there was so much contact with my office and me directly,” he said. “A lot of friends I’ve worked with opposed it, (fearing) the implications for Israel.”

“At times I was in listening mode,” he said. “And then I asked my own questions. I always asked the folks opposing the deal, ‘How do you stop the bomb now, in the next six months?’

“The opponents asked, ‘What happens in the out years?’ when the constraints are lifted after 10 to 15 years to permit Iran to have a (supposedly) peaceful program. ‘What if they have an industrial strength civilian program and all of a sudden they make a sharp turn? How do you stop them?’”

These questions go to the heart of the debate.

For proponents of the deal, the need to stop Iran from getting a bomb in the short term outweighed other issues. By the time President Obama took office, Tehran had enough fissile material, in principle, to make a bomb. On George W.’s watch, Iran moved from an estimated 164 centrifuges to around 5,000. It was already too late to wholly eliminate Iran’s enrichment program.

By the time of the interim accord, in 2013, 19,000 centrifuges were spinning and Iran was only one to two months away from breakout. Ayatollah Ali Khamenei stated this week that, had Iran not made “concessions” in the deal, “in a short time we could have reached 50,000 or 60,000 centrifuges” while continuing 20 percent enrichment (nearly bomb grade) and speeding up development of advanced centrifuges.

There was no time to lose.

Most experts believe this deal will halt Iran’s march toward a bomb for at least a decade — despite the risk of Iranian cheating. It will sharply reduce the number of centrifuges, along with the enrichment and stockpiling of uranium. It will also shut down the plutonium pathway.

That’s why Casey — along with many top U.S. and Israeli security experts — endorses the deal.

However, the senator acknowledges the concerns of those who worry about what happens in the out years, when restrictions start to be lifted. He, too, is concerned that sanctions relief will enable Iran to funnel huge additional sums to bad actors such as Hezbollah, Hamas and Shiite militias in Iraq.

These concerns, he argues, require Congress, to bolster the deal, not thwart it. Our European allies, along with Russia and China — and Iran — have made clear they are unwilling to return to the bargaining table, and are ready to lift sanctions. So demands by GOP candidates — or the Israelis — to reopen negotiations, are pointless.

Instead, says Casey, the administration — with congressional backing — should work with allies to interdict illegal Iranian arms shipments and build up the counterterrorism capacity of allies. Close intelligence sharing will be essential, and sanctions on Iranian support for terrorism will remain.

To prevent Iran from developing nuclear weapons in the long term, Casey says a strong U.S. deterrence policy will be essential, making clear to Tehran that “if you have a weapon we will strike you.” He adds that the United States will have international legitimacy to take a tough position because it will have tried diplomacy first.

Obama has said “all options will remain on the table.” But Casey believes “the language the commander in chief uses should be more specific.”

Hillary Clinton used tougher terms than Obama in an Iran speech this week, stating that she “will not hesitate to take military action” if Iran seeks to obtain a bomb. Others have suggested a congressional resolution authorizing Obama and future presidents to use force if needed to prevent Iran from becoming a nuclear weapons state.

Such a strong stance would require a bipartisan effort, says Casey. “You can’t spend the next 10 years attacking the deal,” Casey added. “Congress can’t be a bystander. We’ve got to get it right.”

Sadly, that hope looks like a pipe dream. There are serious GOP thinkers in Congress, but they appear cowed by political gamesmen. Do Republicans really value sound bites more than thwarting an Iranian bomb?