The Chief Commander of the United States military is the President, who is the Chief Executive of the executive branch of government. The power of the executive branch is limited by the U.S. Constitution by the creation of the other two branches of the Federal government, the Legislative (comprised of the two houses of congress: senate and house of representatives) and the Judicial (comprised of the United States Supreme Court and all the lower courts.) Each of these three branches were established to operate as checks and balances against the accumulation of too much power by any one of them.
It is interesting to note that despite all this codifying of the powers that be the President is essentially invested with unlimited powers in 'wartime.' With the advent of the so called War on Terrorism we see an executive branch that has deliberately created a global environment of fear and terror within which it has absolute power, unbridled or hindered by anyone. And that dear readers is a prescription for tyranny.