This is exactly what SHOULD happen. On U.S. soil troops are subject to posse comitatus. The second they step foot into Mexico they can possess and hold territory with force if necessary. The Bush Doctrine allows for just that if Mexico control its border.
No.They are only restricted from being used as LEO's against (US) Americans. That leftist talking point has been shot down more times than J. McCain. He's still dead BTW!