Fred Kaplan's article on the McChrystal dust-up is worth reading. He encourages Obama to also can both the U.S. ambassador, Gen. Karl Eikenberry, and Richard Holbrooke, the U.S. envoy to Afghanistan and Pakistan. A taste:
Petraeus...gains enormous leverage, should he decide to use it. A year ago, Obama, at the urging of Secretary of Defense Robert Gates, relieved Gen. David McKiernan of command in Afghanistan in order to hire Gen. McChrystal, who seemed more suitable for the new strategy. Obama would find it extremely difficult to fire Petraeus, who is much more of a household name, a year hence, even if he had good reason to do so.
That's Ricks' view too.