As Trump seeks to wind down the war in Iran, the United States is facing not only economic fallout such as higher gas prices but also mounting geopolitical costs. Fresh disputes between Washington and NATO over the Middle East conflict are pushing European leaders to seriously consider a future in which the U.S. no longer leads the alliance.

Trump’s decision to leave NATO in the dark before launching strikes on Iran — as well as his subsequent call for the alliance to assist in reopening the Strait of Hormuz — has inflamed tensions that had been simmering for months over the president’s threats to seize control of NATO-linked Greenland and Canada, along with repeated suggestions that the United States might withdraw from the alliance entirely.

“Something fundamental has broken,” says Ivo Daalder, a former U.S. ambassador to NATO under President Barack Obama. Trump, he says, doesn’t believe America’s security depends on the security of Europe — a position that defies decades of foreign policy logic going back to the end of World War II, when NATO was founded by the U.S., Canada and their European allies to provide a bulwark against Soviet aggression.