Shiite militias, backed by Iran, are now perhaps the gravest source of instability in Iraq. This Knight-Ridder article suggests that U.S. generals knew that their presence was growing but did nothing. Why? Because this administration has committed itself to its own spin, at the expense of a commitment to our national security:
Acting against the Shiite militias would have undercut the administration's arguments that foreign terrorists and holdovers from Saddam Hussein's regime were the problem in Iraq. It also would have raised doubts about the administration's reliance on training largely Shiite security forces to replace U.S. troops in Iraq.