Existing sanctions made it so difficult, in fact, that some wonder why the administration has bothered with the designation at all. “We do not need to do this to maximize economic pressure on the IRGC, or Iran, for that matter,” Richard Nephew, who was the sanctions expert for the team that negotiated with Iran under President Barack Obama, wrote in an email. The Treasury sanctions, plus a 2010 law called the Comprehensive Iran Sanctions, Accountability, and Divestment Act, mean “only the incorrigibles” would do business with anyone they suspect of IRGC ties—major companies avoid them anyway. “In the Obama administration, this was enough to prove to us that this was not worth doing. Then, when we got into the possible negatives—including what this might mean should IRGC forces and U.S. forces be operating in the same space … we concluded this might do more harm than good.”

Mark Dubowitz, who heads the hawkish Foundation for Defense of Democracies and has advised the Trump administration on Iran policy, advocated for the new designation, and argues that it makes a big difference. “This just layers on top of all of the current sanctions an additional and more expansive, punitive measure that will deter more business and, I believe, diminish current business that’s still ongoing between the Europeans and the Iranians, and the Asians and the Iranians,” he told me.

As for the question of what it means for U.S. troops, Iranian Foreign Minister Javad Zarif called for designating U.S. Central Command, which oversees American forces in the Middle East, as a terrorist organization—implying that Iran would view them as targets just as they’d view, say, ISIS members. Maybe that’s bluster, but it introduces a volatile dynamic at a moment when, following the fall of the caliphate, U.S. forces and Iranian forces and proxies are competing for influence in Syria and Iraq, said Ariane Tabatabai, an associate political scientist at Rand. “Iran doesn’t have as much to lose as it had in the past,” she told me. Tabatabai noted that one IRGC-affiliated account on social media had suggested targeting U.S. contractors—one potential way of escalating without hitting American troops directly.

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Indeed, this possible risk was what helped prevent an FTO designation in the past. When the Treasury Department made its own terrorism designation against the IRGC in the fall of 2017, then–Secretary of State Rex Tillerson explained that the position of U.S. troops was a reason not to go further. “There are particular risks and complexities to designating an entire army of a country,” he said at the time, adding that it “would put in place certain requirements where we run into one another in the battlefield, and it would trigger actions that are not necessarily in the best interests of our military actions.”