“Neither the president nor I have any illusions that direct dialogue with the Islamic Republic will guarantee success,” Clinton will say, according to excerpts of a speech she is scheduled to give to the Council on Foreign Relations at 1 p.m. “But we also understand the importance of trying to engage Iran and offering its leaders a clear choice: whether to join the international community as a responsible member or to continue down a path to further isolation.”

Clinton, however, will reiterate that time is running short for Iran to respond.