Do you recall the incident where a young lady, a U.S. citizen by the way, was shot and killed in San Francisco by an illegal immigrant?  That illegal immigrant was about to be deported by federal  immigration officials for the 6th time but first gave him to San Francisco because SF wanted him on a drug related warrant.  The federal officials requested an "immigration detainer" (request to be notified before they release him).  San Francisco officers  did NOT notify the feds because SF is a sanctuary city.  That man went free and later shot the woman while she was walking with her father.

Here, the feds cooperated with the local SF authorities and the local authorities refused to honor their request.   That young lady could have been you.

Still want "sanctuary cities"?