Treaties are subject to the advise and consent of the Senate under the U.S. Constitution. For some time, U.S. officials in Iraq have been negotiating what amounts to a Status of Forces Agreement (SFA) with Iraq counterparts. This document would cover the status of U.S. bases in Iraq, and also govern the legal structure under which military personnel operate in Iraq. Typically, the host country would allow most crimes to be be tried by the U.S. under the Uniform Code of Military Justice, and that would be spelled out.
I have long felt that an SFA was important to a mature relationship with the Iraqi government. Since it would specify the permissible realm of American activities, it might help to curtail the wholesale arrests of Iraqi men who happen to have a mustache (most do).
The issue here is whether the Bushies are attempting an end run around the Constitution.
Secret US plan for military future in Iraq | World news | The Guardian