Aside from the laughably imprecise commitment embodied in George Bush's latest understanding with Iraqi PM al-Maliki about when US troops will leave --
a general time horizon for meeting aspirational goals
it should also be noted that the new understanding also cites --
progress made toward completing a broad strategic framework agreement that will build on the Declaration of Principles signed last November
The very first principle of which is that the US endorses
Supporting the Republic of Iraq in defending its democratic system against internal and external threats.
an open-ended defence commitment (there will always be some "enemy") that in any other context would be the subject of a treaty and therefore require Senate ratification. Thus Bush's response to his apparent concession of agreeing any timeline for being out of Iraq is to rub the Senate's nose in his intention to do an end-run around his constitutional obligations. One of the many questions is whether he's attempting to constrain Barack Obama's visit to Iraq.