The alleged Iranian plot would make great material for a spy novel, but it would go against Iran's own interests and past behavior
It's entirely possible that U.S. Attorney General Eric Holder's announcement today is exactly what it looks like: the U.S. discovery and foiling of a plot by Iranian government agents to assassinate the Saudi ambassador to the U.S. in a bomb attack, possibly in Washington, DC. Iran has a record sponsoring terrorism, and Iran-Saudi competition can sometimes look like a Cold War of the Middle East. But, for all the plausibility that Iran might be willing to blow up a Saudi ambassador, it's not at all apparent what they would gain from it. Iran has never been shy about sponsoring terrorism, but only when it was within their interests, or at least their perceived interests. It's hard to see how they could have possibly decided on a plot like the one that Holder claimed today.
What would it really mean for Iran if the Saudi ambassador to the U.S. were killed in a terrorist attack in Washington? The U.S.-Saudi relationship has been bad and getting worse since the start of the Arab Spring, with the Saudi monarchy working increasingly against the democratic movements that the U.S. supports. A senior member of the royal family even threatened to cut off the close U.S.-Saudi relationship if Obama opposed the Palestinian statehood bid, which he did. If the U.S. and Saudi Arabia really broke off their seven-decade, oil-soaked romance, it would be terrific news for Iran. Saudi Arabia depends on the U.S. selling it arms, helping it with intelligence, and overlooking its domestic and regional (see: Bahrain) abuses.
If the U.S.-Saudi alliance fell apart, the Shia-majority Islamic Republic of Iran would have an easier time pushing its regional influence against Saudi Arabia, especially in some of the crucial states between the two: Iraq, Bahrain, and the United Arab Emirates. Iran would be able to reverse its increasing regional isolation and perhaps flip some Arab leaders from the U.S.-Saudi sphere toward its own. The best part of this, for Iran, is that it probably wouldn't even have to do anything: the U.S.-Saudi special relationship, if it collapses, would do so without Iran having to lift a finger. The dumbest thing that Iran could possibly do, then, would be stop the collapse, to find some way to bring the U.S. and Saudi Arabia back together. For example, by attempting to blow up the Saudi ambassador to the U.S. on American soil.
The Iranian leadership, for all their twisted human rights abuses and policies that often serve the regime at the cost of actual Iranians, are not idiots. Though they use terrorism as a foreign policy tool, the attacks in Iraq and Lebanon and elsewhere have clearly been driven by just that -- a cool-headed pragmatic desire to further Iranian foreign policy interests. Unifying the U.S. and Saudi Arabia at a time when they are drifting apart with a plot that would galvanize American publics and policymakers to support Saudi Arabia, and all without actually doing much strategic damage to either country, would be monumentally stupid. They've made serious, ideology-driven mistakes before -- as government often do -- but this plot comes so far out of left field that it should raise more questions than accusations.
If they would go through all the trouble to organize a bombing attack on U.S. soil -- no easy thing to do -- why target someone so low-level? For that matter, why launch an attack on U.S. soil at all, something Iran has never done in the tumultuous decade since September 11? Why now, as opposed to, for example, during the height of the Iraq war? Why incur the wrath of the U.S. now, so soon after releasing the U.S. hikers detained in Tehran? (Their release was a modest and long overdue concession, but one that suggests the path of Iranian diplomacy.)
And why get involved with Mexican drug cartels? Is that really someplace where Iran has good contacts these days? As Ken Gude of the Center for American Progress asked, "Wiring money into US? Talking about plot on phone? Does that sound like an intel service to you?"
All that said, it really is possible that this is exactly what Holder says it is. Stranger things have happened, and Iran may have simply made an enormous, if out-of-character and obviously self-hurting, blunder. It's also possible that the two Iranian men really were planning to bomb the ambassador, but are either rogue members of the Revolutionary Guards or not really members at all. Clearly, there is much more information in this story that has not yet been made public. Maybe that information, if it ever comes out, will back up the official U.S. version -- which the White House already says it will use to escalate sanctions -- and maybe it will tell a different story. But the plot as we now know it doesn't seem like something that Iran's leaders would think was a good idea.
Update: Colleague Steve Clemons has a smart response to this post, explaining Iran's possible logic in launching such an attack.