Iranian President Hasan Rouhani is due to address the United Nations General Assembly Tuesday in New York. With him comes a sense that progress may now be possible in U.S. relations with his nation. Similar visits from Rouhani's predecessor, Mahmoud Ahmadinejad, were met with dread: His speeches were anti-American, anti-Semitic, anti-logic rants. But Rouhani seems more open, and this must be endorsed by his boss, supreme leader Ayatollah Ali Khamenei. A recent exchange of letters between President Barack Obama and Rouhani are part of the thaw. Iran, because it has defied the world with its nuclear program, faces sanctions that keep it from selling oil and executing crucial banking transactions. Rouhani is signaling Iran might deal on the nuclear program if the sanctions end. That's a possibility Obama should pursue with determination and care.