Two senior administration officials confirmed to us that U.S. soldiers and Shiite militia groups are both using the Taqqadum military base in Anbar, the same Iraqi base where President Obama is sending an additional 450 U.S. military personnel to help train the local forces fighting against the Islamic State. Some of the Iran-backed Shiite militias at the base have killed American soldiers in the past.

Some inside the Obama administration fear that sharing the base puts U.S. soldiers at risk. The U.S. intelligence community has reported back to Washington that representatives of some of the more extreme militias have been spying on U.S. operations at Taqqadum, one senior administration official told us. That could be calamitous if the fragile relationship between the U.S. military and the Shiite militias comes apart and Iran-backed forces decide to again target U.S. troops.

American critics of this growing cooperation between the U.S. military and the Iranian-backed militias call it a betrayal of the U.S. personnel who fought against the militias during the 10-year U.S. occupation of Iraq.