With less than a month to go until the U.S. midterm elections, Iran is escalating attacks in the Strait of Hormuz, dramatically reducing the amount of oil moving through.

The uptick follows celebrations by the Trump administration that U.S. naval escorts had allowed oil flows to reach nearly prewar levels. But last week, Iranian attacks hit at least nine vessels in the strait — a level of attacks on shipping not seen since July, when the United States began encouraging ships to make the transit without permission from Tehran, according to data from the United Nations and maritime tracking firm Kpler.