Who gives the order?

With US forces poised to storm Najaf's Imam Ali Shrine, something many experts consider to be a very bad idea indeed I just want to know who has decided to do this. I know there's a pre-occupation with politicians over-ruling generals, but this is an action with massive political consequences.

If it goes wrong the whole Iraq project could be in danger. If it goes right someone might get to look a hero. However it's five minutes to this particular midnight and no-ones put their head over the parapet. The local Iraqi governor has invited in the US Marines, but the Iraqi government appears somewhat split on the issue. Meanwhile since it's US troops there has to be a US agreement about this somewhere. Is it Abizaid's call? Negroponte's? Rumsfeld's? Bush's?

All I'm saying is I want to know who's idea this was and who's given the go-ahead.