I don't think Detroit, the Dakotas or even Detroit for sure has offered refuge and by extension open invitation to illegals orally or in writing the way cities like some of the Californian cities have.
Trump is saying to the sanctuary cities 'You want it. You got it.'
Apparently some of the better off progressive celebrity types like Cher are noticing
the benefits of open border policies 
getting uncomfortably close to the estate and are rethinking their "champions of diversity" status.