In the Summer 2010 issue of Parameters, the War College quarterly, there is an historic overview of the involvement of U.S. military officers in politics. According to the author:

The belief that the American military has been uninvolved in politics is traditional and long-held. In his magisterial work on the subject of civil-military affairs, Samuel P. Huntington stated flatly that “after the Civil War officers unanimously believed that politics and officer-ship did not mix.” This article has attempted to show that such an assessment is simply not true. Rather, senior military officers were continually and deeply involved in political affairs both before and after the Civil War. More importantly, such a relationship was not seen as either un-American or unconstitutional. On the contrary, for most of the nation’s history the close relation between soldiers and politics has been encouraged and accepted.
The article can be read by clicking here.