What Should Obama Do Next on Iran?

As Congress returns to Washington after Labor Day, the vote on the Iran nuclear deal will be its most important since the decision to go to war in Iraq in 2003. While Republicans dominated the debate in July, Democrats regained lost ground in recent weeks with a flurry of endorsements in both houses of Congress. I testified in favor of the agreement before four congressional committees, and talked with many members individually during July and August. It now appears almost certain that President Obama has the votes to prevail in Congress.

With geopolitical stakes as high as they are, we had a right to hope for a more genuine, sober debate. Instead, on a war-and-peace issue that will affect American power in the Middle East for a generation to come, not a single one of the 301 Republicans in the Senate and House is likely to vote for the deal. The only real debate in Washington is in the Democratic Party, and only a small number of its members will defy the president and vote against the deal.

Mr. Obama has managed to persuade most Democrats that, however imperfect, there is no effective alternative to a deal that will freeze Iran’s nuclear apparatus for more than a decade by diplomacy rather than another Middle East war. Republicans, by contrast, did not make the case to enough Democrats who were genuinely on the fence that walking away unilaterally in hopes of a better deal later was realistic.

Though rejecting the deal would only strengthen Iran and weaken America’s global credibility, Republicans have been right to highlight the deal’s principal weakness — it could permit Iran to emerge stronger 10 to 15 years from now as restrictions on its nuclear program begin to lapse. Specifically, an unfettered Iran in 2030 would be free to reconstitute an expanded civil nuclear program. It could possibly use that program, as it has in the past, to build a covert nuclear arms effort. This is one of the deal’s major downside risks that the Obama team has struggled to counter.

Whether Iran gets that far will depend ultimately on the leadership and will of the United States to stop it. That is why Mr. Obama needs to affirm what has been missing in the Iran debate: a comprehensive United States strategy to contain Iran’s support for terrorism and to prevent it from becoming a nuclear weapons power. As with the Truman Doctrine, where the United States vowed not to let Greece and Turkey go Communist in the late 1940s, Mr. Obama should declare that he and his successors will not permit Iran to go nuclear. This won’t win him many Republican votes in the short term, but it will be a serious response to their concerns and reassure wavering Democrats. More important, it is the right response to an assertive Iran and will recoup some of our diminished credibility in the region.

Mr. Obama should not be content to have his veto sustained in Congress. His more important aim, looking beyond the vote, is to win the long-term struggle with Iran for power in the Middle East.

To begin this effort, the administration should commit to a policy of coercive diplomacy — major steps to keep Iran on the defensive and push back against its growing power in the Middle East. The president should suggest that Republicans and Democrats agree on a separate resolution to support this more tough-minded approach. Such a resolution could begin to heal the wounds from the bruising Iran debate and to chart a more assertive American posture in the region.

A new, bipartisan policy should include the following elements. First, Mr. Obama could reaffirm President Jimmy Carter’s doctrine from the 1970s that the United States will defend its vital interests in the security of the Persian Gulf region against any aggressor. This would bolster the recent efforts of Secretary of State John Kerry to strengthen the defense of Saudi Arabia and the gulf states.

Second, Mr. Obama could state in unmistakably clear terms that the United States would use military force to strike Iran should it violate the nuclear agreement and drive toward a nuclear weapon. This would be an important reassurance to the many members of Congress in both parties who want to see the nuclear deal not as an isolated initiative but as an integral part of a larger and more assertive American regional policy.

Third, Mr. Obama could announce the expedited renewal this autumn of the United States-Israel military assistance agreement, set to expire in 2017. This would counter Iran’s support of Hezbollah and Hamas in challenging Israel’s security on its northern and southern borders. Mr. Obama could commit to ensuring Israel’s qualitative military edge over Iran and other regional rivals. He should close the glaring public gap between him and Prime Minister Benjamin Netanyahu. A strong symbolic step would be for Mr. Obama to travel to Israel to stand side by side with Mr. Netanyahu against a nuclear Iran.

Finally, the administration could reaffirm America’s commitment to form a strong regional coalition with moderate Arab states, Turkey, the European allies and our Asian allies to reimpose sanctions on Iran, should that be necessary. This United States-led coalition could also be useful in pressuring Iran politically to end its support for the bloody regime of Bashar al-Assad in Syria.

As Mr. Obama and congressional leaders look beyond the Iran vote, the reassertion of a stronger American presence in the Middle East could earn bipartisan support.

An Obama pivot back to American leadership in the Middle East is not only good politics in a divided Washington, but also the right diplomatic response to reaffirm United States power and purpose on Iran and in a violent, turbulent but still vital Middle East.