I see it as the American version of that old Canuck favorite — the garrison mentality. In the Canadian context, the garrison mentality refers to our fear of an all-powerful Nature as the Other, the Alien that must be eradicated to make civilization safe for us. Probably, though, we fear that it is ourselves as the intruding Other who must defend itself from the rightful "natives," both Nature and the First Nations.
The Americans, having taken a more aggressive and “successful” role in pushing back the Other, have only now reached their "garrison moment." They have shored up their borders and are now desperately defending them to preserve the hard-won spoils for themselves.