The Washington Post reports: The expanding U.S. military campaign against the Islamic State group in Iraq relies in part on an uneasy, arms-length partnership with Shiite militias backed by Iran — organizations that were once relentlessly effective killers of U.S. troops.

Now, as the campaign enters its second year, there are signs that this awkward alliance may be fraying: militia threats of renewed attacks on U.S. personnel, a greater U.S. effort to bolster Sunni forces that are traditional adversaries of Iran and accusations that the U.S. air campaign has at times targeted Shiite forces.

The shared desire to defeat the Islamic State appears to be enough so far to keep the militias and the Americans working in common cause. But officials and experts said both sides know that their broader regional objectives are in conflict. [Continue reading…]