In 2014, the Hill newspaper rated Minnesota the second-most-liberal U.S. state. For decades, Minnesotans had reliably supported Democrats in the House, in the Senate, and for the presidency—in Ronald Reagan’s landslide presidential reelection of 1984, it was the only state in the country to support his opponent, former Minnesota Sen. Walter Mondale.

Yet in 2016, America’s second-most-liberal state did something unexpected. As the presidential campaign rolled on, Donald Trump picked up a surge of support, drawing level with his Democratic rival, Hillary Clinton. In the end, Trump bettered Clinton in 78 of the state’s 87 counties. While Clinton eked out a narrow victory in the state by a 45,000-vote margin, it came almost entirely from the state’s largest city, Minneapolis.

On the morning of Nov. 9, 2016, progressives in Minneapolis woke up to find themselves on a lonely island of […]