Within hours of revealing a foiled plot by Iranian officials to assassinate Saudi Arabia's U.S. ambassador on Tuesday, the Obama administration pledged to impose additional sanctions on Iran and further isolate the country. Now the U.S. is trying to make good on that promise. State Department official Wendy Sherman tells Foreign Policy's Josh Rogin that President Obama, Secretary of State Hillary Clinton, and other top diplomats have spent the past 48 hours calling every single capital in the world (if true, that's a couple hundred phone calls) to encourage them to make sure Iran's elite Quds Force "stops doing business in their countries, to look at high-level visits that might be coming from Iranians to their country, and to consider, let's say, postponing, if not cancelling outright, those visits." The U.S. approach seems like the diplomatic equivalent of sending Iran to timeout until it can cool off. But there are questions about just how far the U.S. can go in retaliating against Iranian officials.

The U.S. is certainly talking tough. In his first public remarks on the alleged Iranian plot on Thursday, Obama promised to "apply the toughest sanctions" on Iran and to "mobilize the international community to make sure that Iran is further and further isolated and that it pays a price for this kind of behavior." Even if top Iranian officials didn't have "detailed operational knowledge" of the scheme, he added, "there has to be accountability with respect to anybody in the Iranian government engaging in this kind of activity." The New York Times points out that Obama said all options were on the table--a "diplomatic signal that he would not rule out military strikes." 

CBS News, meanwhile, reports that Susan Rice, the U.S. ambassador to the U.N., met with Iranian officials at Iran's mission to the U.N. on Wednesday, in what CBS calls a "highly unusual contact for two countries that do not have diplomatic relations." (The Times says Rice presented her Iranian counterpart, Mohammad Khazaee, with a letter.) During testimony on Capitol Hill on Thursday, Treasury Undersecretary David Cohen said the U.S. was considering sanctions against Iran's Central Bank.

When push comes to shove, however, the U.S. may not have much leverage in responding to the assassination plot. The Times notes that "administration officials privately say it is highly unlikely that the United States would respond with force." Since the U.S. hardly does any business with Iran, the paper adds, the U.S. can't impose unilateral sanctions with  teeth. That means the U.S. will need to get international players like Russia, China, Europe, and India on board--a strategy that has long proven difficult because Russia and China have commercial ties with Iran and especially its energy industry (punishing Russian and Chinese companies that do business with Iran, as some U.S. lawmakers are now demanding, would also be dicey). Targeting Iran's Central Bank would likely "provoke resistance because it would entangle other countries or entities that do business with the central bank," The Times explains. "Another possibility would be to focus on members of Iran's Revolutionary Guard Corps who are involved in the country's oil industry. But that could affect global oil markets."

Time's Tony Karon sums up the dismal outlook for substantive movement on Iran very well today:

The plot allegations, in short, are unlikely to be a game changer in the long-running effort by the U.S. and its closest allies to isolate and pressure Iran over its nuclear program: Those already on board with that effort--such as Britain and France--are backing U.S. calls for action on the embassy plot; those skeptical or opposed to that effort appear less certain of just what the evidence presented thus far by the Administration actually means.