Let’s go back a few years and reset some make-believe headlines: to protest his ruinous state-run health care plan, Republican mayors announce a boycott of President Obama’s annual meeting with big-city leaders.

“Insult to first black president,” the New York Times would scream. “Mayors show disrespect for son of Chicago,” howls some other member of the liberal media establishment. “A chance to discuss issues with a sitting president is not to be wasted,” HuffPost would huff.

Now, flip the calendar to 2018, and the announcement that some left-wing mayors would not attend President Trump’s scheduled reception for mayors to protest his administration’s desire to follow the law and root out illegal immigrants holed up in so-called sanctuary cities.

In at least one respect, Trump caught a break: one of the no-shows is New York’s showboating Mayor Bill de Blasio, who decried the Justice Department’s “racist assault on our immigrant communities. It doesn’t make us safer and it violates America’s core values.” A chance to avoid contact with de Blasio is on the same level of luck as being told your scheduled colonoscopy can be deferred for five more years. Besides, he’s always late.

De Blasio, of course, is testing the waters to see if he can outdo Sen. Bernie Sanders and Elizabeth Warren among far-left Democrats for a potential 2020 presidential run. Siding with illegal immigrants against law enforcement agents comes naturally to de Blasio. This is the same mayor who showed such utter disregard for New York’s finest that officers turned their backs on him as he spoke at a memorial service for two cops gunned down in the line of duty.

What’s at stake here is not hard to understand: cities like San Francisco, New York, Chicago, and Los Angeles are taking unilateral steps to thwart Trump’s promise to round up and expel dangerous criminals who have taken brazen advantage of the native kindness of Americans.

The notion that mayors are putting their cities’ police departments in conflict with federal agencies like ICE – Immigration and Customs Enforcement – is the kind of reckless political grandstanding that can get someone killed. Will the feds and the local cops draw guns on each other? Will the city’s men and women in blue protect illegal immigrants with force against ICE agents if ordered to do so?

As cities pull away from enforcing federal laws about immigration, it’s easy to foresee the circumstances that could lead to a cop on cop confrontation. Let’s not let that happen.