Supporters of moderate cleric Hassan Rohani hold a picture of him as they celebrate his victory in Iran's presidential election in Tehran June 15, 2013. (Reuters/Fars News/Sina Shiri)   Rarely in the past half-century has diplomacy so transformed international relations that it promised an end to deep, seemingly intractable conflicts. Our world was fundamentally changed for the better by Nixon’s opening to China in 1972 and Reagan’s embrace of Gorbachev in 1986. The decision by Iran to reach out to the United States and break more than thirty years of hostility offers an opportunity that is equally significant. It could defuse many of the conflicts now tearing apart the Middle East.

The historic phone call between President Obama and President Rouhani, together with the meeting between Secretary of State John Kerry and Foreign Minister Mohammad Javad Zarif, has set the stage for new negotiations over Iran’s nuclear program. Tehran, which has made it clear that it seeks the lifting of economic sanctions against the country, will lay out its road map in Geneva.

The Obama administration must move with similar diplomatic ambition. It should ignore the usual warnings from the usual sources about succumbing to a “charm offensive” meant only to buy Iran time to develop nuclear weapons. This is not the time to insist on old conditions that violate the spirit of equitable negotiations, but for constructive reciprocal action that can reinforce Iran’s need for compromise. Before the next meeting, the administration must acknowledge Iran’s right to uranium enrichment and lift those sanctions that prevent it from trading in everyday goods and services, especially medicines and other basic necessities.

There are two overriding reasons for a bold US response. First, Iran’s opening is a reflection of the democratic will of its people, as expressed in the June elections, which demonstrated that Iranians want to rejoin the full international community and develop their economy unhampered by the sanctions they have endured for a decade. But there are limits to this popular support for constructive engagement and to the leadership’s embrace of it. It is conditional on US acceptance of the legitimacy of the Islamic Republic and its right to a peaceful nuclear program. And it is limited by the fact that hard-line regime elements would be happy to use a lack of US good faith as a reason to roll back this democratic-based opening.

Second, the United States has much to gain from improved relations with Iran and little to lose from easing sanctions. Even after Russian President Putin’s diplomatic rescue of Obama’s jumbled response to the Syria crisis, US policy in the Middle East is still in trouble. Not only would good relations with Iran put to rest worry about a war over Tehran’s nuclear program; it would help advance many other US goals in the region. It could facilitate the American withdrawal from Afghanistan; help stabilize Iraq and curb the increase in sectarian violence there; and improve the chances of a negotiated conclusion of the Syrian civil war, which could prevent Syria from becoming a haven for Islamist extremists—a goal shared by Washington and Tehran. More broadly, better US-Iran relations could take much of the poison out of the regional Sunni-Shiite divide, and give the United States more power to curb the irresponsible policies of Saudi Arabia and other Gulf states that have fueled Sunni extremism.

In international relations, there is a time for pressure and a time for high-minded action. Once engagement begins, one positive action can beget another; one constructive move can lead to another. We saw this in the opening to China and in the process that led to the end of the cold war. That is what the Obama administration must do now vis-à-vis Iran.

With a US-Iranian rapprochement possible, Bob Dreyfuss blogs about Israel’s increasingly sidelined influence.