I think American police department capabilities may be underestimated. In the area I worked in, in critical situations, we could call on one large and one small city pd, numerous sheriff's offices, the BLM cops, several tribal police departments, the wildlife guys, the local FBI office, the state police and if things really got bad, the state pen special guys. There were always a number of special trained officers on normal patrol and (I have been gone a few years) I would assume that now there are a number of officers who have been to Iraq and Afghanistan. Everybody had pistols and shotguns and all the state police had AR-15's. Given more time, swat teams from all over the state would be there too.

There would be tremendous confusion and hell to pay in the first few hours but there is more capability there than people may think. Those Mexican drug assassins in Arizona certainly didn't have things all their own way.