Dr. Hohn's Article.
The politicians did not lose Vietnam by interfering with the military and did not win the Gulf War I by staying out of the way. The reasons for our defeat in Vietnam do not have to do with the politicians directing the military. Those causes are a very deep and broad topic way too much for one full volume let alone a single blog. Likewise it wasn't the politicians keeping their noses out of the war planning in the Gulf War I that lead to a decisive victory there.
A major spur to the military becoming politicized occurred in the '60s and '70s. The Democratic Party acquired a distinct anti-military flavor and this drove many officers to the Republican party which filled the void left by the Democrats. Those Democrats who continued to support the Military became marginalized in their own party.
Donald Rumsfeld (the controversy over inspired all of this research, reading, and writing) is secretive with the military which is both a bad and necessary thing. He is charged with transforming the military to get it into line with modern realities. He needs to be secret so Pentagon opponents of reform can not work to derail those plans. Of course, this means he may not seek adequate input from the military which was one of the things that led to the "don't ask/don't tell" fiasco.
Colin Powell does not come out of the article at all well. The only compliments Mr. Powell gets is being very adept at politics and getting what he wants. In fact, Dr. Hohn believes Powell's presence in the Bush Administration dictated a strong character in another cabinet position (and I assure you that position is not Secretary of Transportation). Mr. Powell kept his disagreements out of the spotlight to a certain degree, but in the end we all knew what his position was.
The Clinton Administration. President Clinton's well known past with respect to the military poisoned the water. In fact, the article characterizes the administration's dealings with the military as fearful and suspicious. Of course, the military shares quite a bit of blame for all of this. This led to the "don't tell/don't ask" fiasco. The Clinton administration did not consult or take advice on the matter and then when the initial policy was announced many officers and military leaders worked via back channels and through their friends and families to defeat the policy.
The military often cooks up plans and alternatives to direct policy makers to their preferred policy.
Here is Dr. Hohn's article in full, it is a pdf document.