Months before Sept. 11, as Rumsfeld began the transformation of the Pentagon, he ran into contumacious obstructionism from the army and its then-Chief of Staff Gen. Eric Shinseki. Shinseki dug his heels in and refused to change much of anything about the Army. Shinseki went as far as to go behind Rumsfeld’s back to the Senate where his political mentor (and long-time family friend, Sen. Dan Inouye of Hawaii) and others backed his play.
But for the political cover Sen. Inouye gave Shinseki, he might have been fired then and there. Civilian control of the military means people such as Shinseki cannot be allowed to play the back-channel political games he played again and again. Shinseki stayed, and the Army went on to spend billions on the Stryker armored vehicle, a Cold War style peacekeeping vehicle that is too big and too heavy to be moved by a C-130 tactical airlifter without being partially disassembled.
Let's review the chain of command, shall we?
President of the United States
(aka the Commander-in-Chief)
Secretary of Defense
Joint Chiefs of Staff
(of which General Shinseki was one)
Note where Shinseki is. If he didn't like the direction, there was an honorable course for him to take - one taken by General Anothony Zinni, who opposed the liberation of Iraq. He could have resigned his commission and then spoken out on the matter. Shinseki was probably familiar with the very lax control of the Clinton Administration (largely due to missteps on gays in the miltiary, the micro-management that led to the firefight in Mogadishu going wrong, and the insult to General Barry McCaffrey), and figured he could get away with it. He then seemed surprised that Don Rumsfeld wasn't going to put up with such nonsense.
In the matter of Shinseki, I think Rumsfeld acted with incredible restraint in not firing him summarily.