Iran and the P5+1 powers have signed a potentially historic agreement to limit Iran’s nuclear program in exchange for the removal of economic sanctions. The accord is a victory for all who favor patient, sometimes frustrating diplomacy over those who favor confrontation, even war. But the latest battle over Iran
policy has just begun. The agreement will face ferocious opposition in Congress from neoconservative hawks, including some Democrats, and from Washington’s allies in the Middle East, Israel and Saudi Arabia. President Obama will need help from Democrats in Congress, and a mobilized citizenry, to sustain a veto of the congressional war party’s rejectionism.

One key question is whether the agreement will become a vehicle for transforming US-Iran relations and realigning US policy in the region, or whether it will become a new source of conflict, with endless disputes over verification and the lifting of sanctions. The complicated details of the accord and the determination of powerful players, foreign and domestic, to sabotage it increase the chances for the latter scenario. The administration and its supporters must therefore not only robustly advance the accord in Congress but put forward a broader strategic agenda on US-Iran relations. (It’s also time to remove the missile-defense weapons placed in Europe under the pretense of protecting the continent from an Iranian attack, and for nations that actually have nuclear weapons to join or comply with the Nuclear Non-Proliferation Treaty, which Iran has always supported.)

Because of the relentless and often irrational opposition to the agreement, the administration was forced to advance it in the most defensive terms: as the best way of ensuring that Iran will not get nuclear weapons, rather than as an essential first step in a broader rapprochement that is not only in America’s strategic interest, but is critical for bringing order and peace to a Middle East now falling into chaos.

That regional realignment would recognize the substantial common interests that Tehran and Washington have in countering ISIS and Al Qaeda; in pursuing a settlement of the Syrian crisis; in stabilizing Yemen and Bahrain; and, more generally, in ending the region’s Sunni-Shia sectarian proxy war. This realignment would also recognize the important role that Russia played—in spite of US hostility arising from the Ukraine crisis—in supporting the agreement. Balancing US ties with Israel and the Sunni Gulf states and better relations with Iran and Russia should strengthen America’s position in the region.

If the agreement is to work as a vehicle for constructive diplomacy, its supporters will have to confront the false alarms about Iran’s regional designs as well as its nuclear intentions. Already we are hearing that lifting the sanctions on Iran will give it more resources to pursue destabilizing and anti-Israel policies. But a reasonable analysis of recent Iranian actions leads to a different conclusion: namely, that the legitimacy of the Islamic Republic rests not on its revolutionary zeal, but on its ability to improve the living standards of its people; that its regional policy is based as much on defensible national interests as it is on anti-Israel fervor; that it has been a helpful partner in Afghanistan and more recently in Iraq; and that it has done more to dampen the conflict in Yemen and Bahrain than has Saudi Arabia, which has resorted to military force in violation of international law.

The Iran nuclear agreement, then, is a bold move to counter the drift toward an unsustainable double war with both Sunni extremism and Iran—and also a new Cold War with Russia, motivated in part by Moscow’s support for the Assad regime in Syria. Obama’s greatest legacy could still be as a peacemaker in foreign policy, but he will have to meet the challenge of not only defending the Iran agreement, but also of making the case for a broader transformation of US-Iran and regional relations.