While Donald Trump is not a politician known for his message discipline, he took the world by storm in 2016 with a well-articulated diagnosis of what ailed the nation. “Make America Great Again” managed in four words to assert that America had been great, that it no longer was, and that he would do something about it. His current campaign, by contrast, has devolved into the litigation of personal vendettas, crass promotion of niche issues like cryptocurrency, and pandering to the donor class on tax cuts and temporary labor. The rallying cry to “Make America Great Again” has become the...