The increasingly intractable conflict between the U.S. and Iran is revealing American military and strategic vulnerabilities — and offering important lessons to its biggest rival. China is watching as the U.S. fails to cut through an Iranian blockade and expends heavy firepower, the Trump administration struggles to extricate itself from an unpopular war, global gas prices soar and the Pentagon’s strategic documents reveal that warding off Beijing is  no longer the top priority . As U.S.