le Carre's fictional Russian spymaster, "Karla." An important question, if a back channel were ever seriously considered, is whether Suleimani's connection with the Iranian nuclear program is significant enough to make him a reliable intermediary. The time for communication may be running out. Economic sanctions are creating a worsening crisis for Iran, one that is a potential threat to the regime's survival. And more potent sanctions are on the way. Meanwhile, Israel, the United States and other allied nations are conducting covert actions against the Iranian nuclear program. Iran called the assassination this week of one of its nuclear scientists another in a series of "malicious terrorist attacks." At some point, the Iranians may conclude that the broad pressure campaign, overt and covert, means that a state of undeclared war exists -- and respond in kind. The Obama administration's squeeze on Iran has been powerful, but also carefully calibrated. U.S. officials insist that America had nothing to do with the recent killing of Iranian scientists, for example, and their denials are credible in part because it would be so difficult for the CIA to direct motorcycle assassins in North Tehran. The pressure campaign has international support, and there's no reason to stop it. But this is a moment when a U.S. emissary should make clear that Iran has a choice -- it can seek to be a nuclear-weapons power or remain an oil power, but not both -- and communicate that to someone who can report directly to Ayatollah Khamenei.