Yglesias downplays the relatively large percentage of Americans who want to cut military spending:
If a President proposed cutting the defense budget and then you had a ton of stories in the press where senior military officers fret off the record that the cuts will endanger America, and every television network trotted out a former general with undisclosed ties to defense contractors as an “independent analyst” to condemn the cuts [...] and if think tank experts who depend on cooperation with the military to do their research either complained about the cuts or else stayed silent, then I think you’d have a giant political fiasco on your hands.
The relevant issue here, in other words, is that the military is the most trusted institution in America and then on top of that the defense sector of the economy has a lot of money and economic reach. Consequently, it’s very political difficult for a president to do anything that provokes the ire of the defense establishment whether or not it polls well in the abstract.
That may be true. But what if someone begins to ask: why do we have tens of thousands of troops still in Germany? And what if the dormant heartland right asks why we need to police the entire world when domestic infrastructure is crumbling, and we cannot afford social security and Medicare. This takes political skill - but I'm sure it could be done. Ron Paul got traction with this in the Republican base. Someone else could build on that. At some point, maintaining a cold War defense posture in a totally different world will require some kind of rebalancing. If nothing else does it, the fiscal crunch will.