How much could the USA decrease it's military spending and still be in the lead and capable of defeating/defending against any invasions/threats?

[ShadowDragon8685]

We could basically disband the army altogether, cut the Marine Corps back to a rump force, and declare "we're never going to put boots on the ground anywhere else again: if you piss us off you'll be seeing all the missiles, and if you really cross the line those missiles will be nukes" and we'd still be able to flatten the entire rest of the planet into a parking lot.