Muriel Bowser, the mayor of Washington, D.C., was born just a year before the city’s residents were given the right to elect their mayor. In the five decades since, Washington has wrestled with challenges common to many U.S. cities, like violent crime. It has also faced challenges that, given its peculiar status under federal law, it shares with no other American city.

But even in Washington’s unique history, there was no episode quite like the one that Ms. Bowser, in her third term as mayor, had to confront on Monday afternoon.

“We know that access to our democracy is tenuous,” the mayor said to reporters just hours after the city’s most prominent resident, President Trump, announced that the federal government was going to take over the local police department and deploy the National Guard to the streets of Washington. “While this action today is unsettling and unprecedented,” the mayor said, “I can’t say that, given some of the rhetoric of the past, that we’re totally surprised.”

Indeed, Mr. Trump has not been shy about his feelings toward the nation’s capital, calling it a “filthy and crime-ridden embarrassment” and “a rat-infested, graffiti-infested shithole.”

For a city that federal law leaves vulnerable to the prerogatives of the White House, the raw rhetoric was a warning. Under the Home Rule Act of 1973, which gave residents the power to elect a mayor and a city council, Washington has a degree of self-governance, but it is limited.