Mayor Mike Johnston’s pointed comments last week about Denverites resisting a federal mass-deportation effort — including a suggestion that he would mobilize the Denver police department to face off with federal and National Guard troops — have generated blowback in Colorado and across the country.

Denver Mayor Mike Johnston dodged a response to President-elect Donald Trump’s “border czar,” Tom Homan saying he would jail the mayor if he does not comply with federal deportation orders of illegal immigrants. Johnston, a Democrat, has been one of ...