Few experts expect Iran to cross Obama’s red line by shutting the strait — an act that could cause global economic mayhem. Nearly 20 percent of the world’s oil supplies pass through the waterway, according to the U.S. Energy Information Administration, which calls it “the world’s most important oil transit chokepoint.”

But a 2012 CRS report authored by Katzman warned that Iran was less likely to shut down the strait entirely than to “disrupt, threaten, harass, and otherwise create substantial instability for shipping in the Gulf.” It added that such “low-intensity” tactics could be a deterrent against “increasing economic, diplomatic, or military pressure against Iran.”

It’s not clear whether the U.S. military would respond to such an Iranian strategy. But it could cost Iran in other ways, by angering oil-consuming countries hit by a spike in crude prices—notably including China, with which Iran has sought closer economic ties.