Donald Trump is a phenomenon. What kind? He seems to think that he is “The Greatest Show on Earth.” And many of his supporters likely agree. That slogan, long identified with the Ringling Bros. and Barnum & Bailey Circus, rings true. Trump may be the P.T. Barnum of current U.S. politics.

A century and a half separates these men, but they are equally big personalities for their times. Barnum and Trump both skillfully leveraged their audacious business methods to become “celebrities.” Barnum, a master showman, also went into politics and even tried his hand at land development.

Barnum and Trump each developed reputations as sharp dealers. They assume a world of caveat emptor, or buyer beware, and are boastful yet skillful debaters. They avoid outright lies — but structured misunderstandings stand as their métier.

They both dealt in landmark curiosities: Barnum in his famous American Museum on Broadway, just south of City Hall in New York City; Trump, farther uptown, at his lavish Trump Tower on Fifth Avenue, as well as many other exuberant buildings and developments around the globe. Just as Trump Tower is a tourist destination, so was Barnum’s museum and, later, circus. He played to the common folk. Trump’s establishments cater to the rich, yet also evoke the fascination of those without money.

Barnum prided himself in never directly lying. In fact, he made money with ambiguous claims about the truth of his exhibits. He relished controversy about his claims to truth — much as Trump thrives on controversy surrounding his truth claims and verbal abusiveness. (Though a recent Politico report counted five dozen statements deemed “mischaracterizations, exaggerations, or simply false” in one week.) ...