One of the foundation principles of American government is that our military is always ultimately under civilian control, with the President as the Commander in Chief acting through his Secretary of Defense.
In general this is a wise policy. From the Roman Praetorian Guard to the present day, military organizations that became powerful and unfettered political organizations within their country or empire have inevitably caused havoc and bloodshed in the end, and often installed and maintained brutal and unprincipled dictators as leaders.
Nevertheless, there is an important division of labor needed here. Civilians should certainly determine the high level policies and objectives for the military, but then they ought to leave the details of the execution to their experienced military leaders. The persistent failure in American politics from Vietnam right through to the current Iraq mess is the tendency for Washington politicians, and particularly Presidents and their Secretaries of Defense, to try to micromanage the military operations they have set in motion, with uniformly disastrous results. During the Vietnam war President Johnson and Secretary McNamara would sometimes involve themselves in the details of the daily Air Force targeting list, and Secretary Rumsfeld meddled continuously in the planning for the Iraq invasion, overruling his experienced generals repeatedly, with disastrous consequences.
These people, if they needed an operation, would never think of going to a politician rather than an experienced surgeon. If they needed a house designed, they would go to an experienced architect, not a politician. Why then are they so arrogant or ignorant as to assume that they know how to manage military affairs better than people who have spent their entire life in the military?
The way the system should work is that the civilian political leaders should determine what the high level military objectives should be, after consulting with their military leaders as to how feasible these objectives are, and then issue the orders to their generals and admirals, and get out of the way and let the military experts do what they have spent their life learning to do. In general, it is the civilians who are often eager to use military power, and the military, who after all are the ones who will have to bury the dead, who are more cautious.
Perhaps there is something about the Washington air that inflates politician’s egos to the point where they fancy themselves experts in everything. In military matters, that is a very dangerous illusion.