I would contend that the Army today is much less political than it was in the period after the Civil War (say 1870 through 1890 or so). If you look at service publications (and the Army and Navy Journal) from that time you'll find any number of political rants, fears about worker uprisings, and other bits and bobs. The Army also found itself entangled in a number of civil uses during that time (riot control and the like) that would not be tolerated today. The Army of that time also recruited from what were considered the "dregs of society," with a fair percentage of the enlisted ranks being of foreign birth (Irish and German mostly, but with a good sample of the other waves of immigrants from that time). It was also physically and socially isolated from American society of the time, and often (at least in the officer ranks) believed that it was superior to that society in terms of conduct, morals, and general bearing. What we're seeing could be taken in some ways as the Army (unwittingly, perhaps) returning to its real roots.

National service is not part of the national tradition by any means. It's always been viewed as a desperation or crisis measure. I think you may be confusing the state troops or militia movements with national service. Those were in theory mandatory but in practice were usually anything but. And in any case, it was always expected that a standing military would exist to provide officer cadre and other support to any "minute man" army. Conscript armies might have been part of the national landscape during the early Cold War and through Vietnam, but they have never been a part of the nation's history on a larger scale. To suggest otherwise really misses the point and leads to a tragic misstatement of the US's military history.