There would have to be a complete retooling of police training if our country descends into a true low intensity conflict. Patrol officers aren't trained or equipped anywhere close to being able to handle coordinated paramilitary attacks. I'd say even most SWAT teams, including many of the big full time units, are not set up to handle large scale terrorist attacks. Really only federal tactical teams like HRT and BORTAC are trained for that kind of stuff. Not only would cops have to have armored vehicles for patrol, they'd have to get extensive training in counter assault, carry rifles to every call no matter how mundane, the days of solo patrol would be over. In short, if we have our own Troubles, American law enforcement would need to more closely resemble European gendarmaries.