Despite the risks, now is the time for Obama and Rouhani to launch the first direct bilateral negotiations since the 1979 Iranian hostage crisis. From Iran's pursuit of nuclear weapons to the conflict in Syria, the American-Iranian rivalry is helping fuel instability in the region.

For Obama, a bold move on Iran would be out of character. After his lurching response to the August 21 sarin gas attack in Syria, critics are declaring Obama's second term listless. A cautious president who focuses largely on domestic issues would have take a major foreign policy risk on talks with Iran, a nation whose leaders have vexed American presidents for decades.

To be fair to Obama, the onus for talks to begin lies with Rouhani. For years, Tehran has rejected signals from the George W. Bush and the Obama administration that they wanted direct talks. And despite all the promising rhetoric from the new Iranian leader, it is still unclear what concessions, exactly, Tehran is willing to offer regarding its nuclear program.

Obama should keep in place the economic sanctions until a comprehensive agreement is reached that ends Iran's enrichment of uranium. He should begin talks but remain firm. In the long-term, negotiations will aid Obama, even if they fail. As he has argued in Syria, exhausting diplomatic alternatives would make it easier to gain American public support to use force if needed.

George Perkovich, a proliferation expert at the Carnegie Endowment, said that the U.S. and Iran should begin bilateral talks focused on a comprehensive agreement on Iran's nuclear program. Talks through the P5 plus 1--the United States, Britain, France, Russia, China and Germany--will, he says, become bogged down.

"We should push for a big comprehensive deal as soon as possible," Perkovich said, "rather than the incremental step-by-step approach. Obama doesn't have the political capital to reduce the sanctions step by step, and Rouhani inevitably will lose political capital."

Perkovich argued that Rouhani and his new foreign minister, Mohammad Javad Zarif, are moderates who have won support for talks from Iran's Supreme Leader Ayatollah Ali Khamenei--for now. Perkovich, who has met both of the new leaders, says they have concluded it is not in Iran's strategic interest to develop nuclear weapons.

"They see that it would totally mobilize the Saudis and everyone else against them," he explained, "and ultimately doesn't benefit them."

Skeptics argue that Rouhani, in fact, represents no change in the regime. They say his call for renewed talks in letter exchanges with Obama, an NBC News interview and an Op-Ed in the Washington Post are ploys. They also dismiss the foreign minister's tweeting a Jewish New Year's greeting. Mark P. Lagon and Mark D. Walllace, two former Bush administration officials, believe the new tone is a ruse to give Iran more time to develop a nuclear weapon.