Iran’s recent elections produced a striking result. In a six-man race, one candidate won an easy victory without the expected runoff. More to the point, Hassan Rohani campaigned for policies of negotiation and engagement with the West, to lessen Iran’s international isolation.

The Supreme Leader gave his blessing — at least for now — by choosing not to interfere in the vote count. The new president, then, appears to have a mandate to engage the United States — if Washington is willing — in practice as well as in words.

Rohani, who officially takes office this weekend, is an experienced, well- informed and shrewd insider in Iran’s leadership. It is too early to know how much he can deliver, but there are positive signs. The Holocaust denier, former President Mahmoud Ahmadinejad, is out of the picture.

Rohani’s 40-year friendship with the Ayatollah Khamenei suggests a level of trust that could make him an effective interlocutor. He knows the nuclear issue inside out. He speaks fluent English. He has broad, popular support. Yet his mandate will be short-lived if he cannot show results.

U.S.-Iranian negotiations, now realistic for the first time in many years, are both more difficult and more important to U.S. interests than any Washington has faced in decades. Just getting started will be difficult.