breaking open the word "cooperate"... 
the intent is to impose a federal function with its legal boundaries and jurisdictions on individuals who are not intended to carry that Federal function.  See the legal battles in a place called Farmers Branch... attempts to turn landlords into an arm of ICE. The alt/right lost that battle and several others in that city to the tune of over a million.  Call it pilot studies on the part of the alt/right....

Turning traffic stops into Immigration status checks was another.... 
That was the issue... how early could a federal function be imposed upon local agencies and individuals. It is an alt/right pejorative term currently used to stigmatize and threaten those who (especially those cities who won the court cases) resisted the imposition of a federal function without a legal jurisdiction.

Cities who comply with statutes for which they do have jurisdiction -- but do not go beyond that limit are currently labelled sanctuary for alt/right reasons.