Michael O'Hanlon tries to find a sweet spot: 

Saving 8 to 10 percent in the annual peacetime defense budget of the United States—arguably the Pentagon’s fair share of a serious deficit-reduction effort—would be hard but not impossible under a shared-sacrifice philosophy. Over ten years, that would translate into $400 billion to $500 billion, to use the decennial accounting popular since the August 2011 debt deal between President Obama and Congress. These cuts would go beyond those already expected as part of a gradual reduction in the nation’s costs for waging war abroad.

… Such cuts, according to my calculations, would avoid going too far. We can avoid salary cuts for our troops and any display of weakening resolve toward East Asia or the Persian Gulf. We can modernize so that our most promising new technologies will adequately equip the forces most likely to fight in key regions. We can retain ground forces large enough, even after the Afghanistan campaign winds down, to carry out another war (heaven forbid) without having to let down our guard in every other part of the world by stealing forces from other theaters.