President Trump has taken extraordinary measures in the nation’s capital to fulfill an ordinary function of local government: keeping clean, orderly streets. His actions seem unusual because government officials in America’s cities long ago abandoned the basics. They have been led astray by academics and activists who promised them crimeless cities and an end to homelessness if only they established a right to housing and eradicated income inequality. These idealistic public-policy frameworks have failed to achieve the desired outcomes anywhere in the U.S. Instead, they’ve ushered in the worst homelessness crisis on record. President Trump’s strategy is straightforward: Everyone living...