The fragmentation would almost certainly occur along ethnic lines; "white" nations would probably arise in the Pacific Northwest and the mountainous, still-heavily-white regions of the old Confederacy. Possibly a Mormon theocracy would arise in Utah.
The lowland South would probably see a black nation, and the native Hawaiians have been talking about independence for some time now. And, of course, Mexico would probably regain much of the Southwest.
Border warfare would be very ugly. Just think Balkans on a continent wide scale. Possibly the worst of it would be Utah vs Aztlan, as the Mormons are (a) demographically expanding, unlike most whites, (b) very, very heavily armed, and (c) living on a piece of land that the Reconquistadores would very much like to reincorporate into Mexico.
Pray it doesn't happen. But brace yourself. Liberal race baiting may yet bring it about.