On May 30, Iraqi special forces stormed the southern edge of Fallujah under U.S. air cover, launching a new assault to recapture one of the last major Iraqi cities under the control of Islamic State militants. Iraq's elite forces who are leading the fight have been trained by U.S. advisers, but many others on the battlefield were trained or supplied by Iran. It's the latest example of how Washington has looked the other way as Iran deepened its military involvement in Iraq over the past two years.

In the lead-up to the assault, Gen. Qassem Soleimani, commander of the Quds Force, the special operations branch of Iran's Revolutionary Guards, met with leaders of the Iraqi coalition of Shiite militias known as the Popular Mobilization Forces.

Sunni politicians in Iraq condemned the involvement of Soleimani and other Iranian advisers in the battlefield preparations, saying it could fuel sectarian tension and unleash a new round of Sunni-Shiite bloodletting. They also cast doubt on the Iraqi government's assurances that the offensive is purely an Iraqi-led effort to defeat Islamic State. "Soleimani's presence is cause for concern," said an Iraqi member of parliament from Fallujah. "He is absolutely not welcome in the area."