A rapid succession of challenges directed at Iran in recent days has reignited a debate in Tehran over how to deal with the rest of the world. Iran's rulers, led by Supreme Leader Ayatollah Ali Khamenei, continue to refuse any negotiations in which they would have to compromise. But an influential faction is now pushing for back-channel talks with the United States as a step toward lowering the tensions raised by U.S. allegations about an Iranian assassination plot. In urging that Iran do more to address foreign criticism, members of the group have also pointed to the rising international pressure...