American officials have expressed hopes that the deal and the economic benefits it could bring to the Iranian people will empower the country’s moderates in a way that could make it easier for the United States to work with them on regional issues.

Whether Iran is interested in changing its regional posture remains an open question.

Iran has long branded itself as the lodestar of the “resistance,” by which it means the regional forces opposed to the United States and Israel. While most members of this alliance are Shiite, Iran has also supported Palestinian groups like Hamas and Islamic Jihad, which are Sunni. And it has spent years investing in proxy forces such as Hezbollah in Lebanon and Shiite militias in Iraq, groups whose rallies are punctuated by chants of “Death to America!” and “Death to Israel!”

For more than four years, Iran has also shown no sign of decreasing its support for Mr. Assad in Syria, despite his growing international isolation because of his brutal efforts to put down an uprising against him.

More recently, Iran and its allies have tried to cast themselves as bulwarks against terrorism, noting that they are fighting the extremists of the Islamic State on the ground in both Iraq and Syria.

Some of Iran’s supporters saw the intense American interest in the nuclear agreement as a de facto recognition of Iran’s strength. They also said the rise of the Islamic State as well as Qaeda-linked groups like the Nusra Front in Syria had led the United States to see Iran as a necessary partner.