Guerrilla warfare? In cities, or rural? Just taking out critical infrastructure?

Yes. Though I would assume that the pressure would mostly be applied to cities and infrastructure. Rural would theoretically be a 'waste' of resources (cities you can easily inflict maximum damage anywhere while rural would be like walking miles door to door for a low impact comparitively... though farms should be on high alert) spreading them thin and putting them squarely into what is the most armed territories of the u.s.