Marc Thiessen is often a panelist on Bret Baier's Special Report. Here interviewed by Fox News' Shannon Bream, he describes the Trump administration's work-around for stymieing sanctuary cities.
Local officials can refuse to honor an ICE detainer, but they can’t refuse to honor a federal felony warrant. So the Trump administration has this thing called Operation Guardian Angel, where they are charging illegal migrants who reenter the country with felony illegal reentry, and then they are presenting the local jurisdictions with federal felony warrants, and they have to hand them over. So they’ve been handing over hundreds of illegal migrants to ICE, and this has set people off.
Outstanding, round up illegals entirely within the law. This has the advantage of labeling those so apprehended as felons who are therefore ineligible for asylum.