The constitutional principle of civilian control is losing its basis in sociological reality: Senior officers are talking to (retired) senior officers about high matters of policy on a regular basis -- and then forwarding their advice to more retired military men with privileged access to the Oval Office.
We owe our present situation more to drift than to design. When making individual appointments, presidents and Cabinet secretaries naturally focus on the abilities of particular candidates. It is easy to lose sight of the overall pattern of appointments. Yet it is precisely this pattern that puts the Founders' commitment to civilian control at risk.
That historic principal has been reasserted in many ways. The Constitution makes the president, not any senior general, "commander-in-chief." The 1947 law creating what is now the Defense Department requires that the Secretary of Defense be appointed "from civilian life." [A temporary change in the law was voted in 1950 to allow retired General George C. Marshall to take the post.] The only statutory position on the National Security Council staff, the staff secretary, is required to be a civilian. The law for the CIA used to require that at least one of the top two slots be a civilian.
These laws did not presume that military officers were unqualified for these positions, but rather that a civilian perspective and ultimately civilian ultimate control was necessary to preserve liberty. There were too many historical examples of generals on horseback becoming dictators. Our lawmakers also wanted to guard against an insular military elite that was separate from civilian life and concerns.
Of course, many senior officers are highly qualified for national security positions, and they should be assigned to those posts as conscious exceptions to the preferred pattern of civilian appointees. But the Senate and presidents should also monitor the pattern of military appointments and try to re-balance toward experienced civilians.