Picture a man with an unquenchable thirst for celebrity, who gets into rows with everybody, who has a gift for punchy quips that make headlines; a man of undeniable charisma who so craves being the center of attention he wants to be the baby at the baptism, the bride at the wedding, and the corpse at the funeral. “While he is in the neighborhood,” one critic grudgingly concedes, “the public can no more look the other way than the small boy can turn his head away from a circus parade!” We speak, of course, not of our current president but of Theodore Roosevelt, based on depictions from more than a century ago.

As a presidential historian, I am often asked which of our past presidents might be best suited for our current moment in time. No doubt it would be Roosevelt. T.R. could surely master our social-media age and especially the Twitterverse with his vivid, memorable aphorisms: “Speak softly and carry a big stick.” “Don’t hit till you have to; but, when you do hit, hit hard.” “It is hard to fail but it is worse never to have tried to succeed.”

Like President Trump, Roosevelt took office in turbulent times. At the turn of the 20th century, the Industrial Revolution had shaken up the economy much as the technological revolution and globalization have redefined our lives today. Big companies were swallowing up small companies. New inventions had quickened the pace of life to a frenzied degree. People in rural areas felt alienated. A menacing gap had opened between the rich and the poor.

Roosevelt looked to the future with what he called a “Square Deal”—for the rich and the poor, the capitalist and the wageworker. Candidate Trump promised to utilize his skill, which he laid out in The Art of the Deal, to bring America back to a simpler time of greatness. But, in the end, the success of any deal depends on the character and the experience of the dealer. No one would argue that either Roosevelt or Trump suffered from a deficiency of bravado or confidence. Yet Roosevelt grew in power precisely because he grew to know his limitations, because he developed the humility to acknowledge his mistakes. After his first, wildly successful term in the state legislature, he developed, in his own words, a “swelled” head. Whenever opposed, he would yell, pound his desk, and retaliate with venom. While his blistering language made great newspaper copy, he soon found himself bereft of support. It began to dawn upon him, he conceded, that he was “not all-important” and that “cooperation from other people” was essential.

That President Trump has not developed such humility is evident. When asked during his campaign whom he consulted on foreign policy, he said, “My primary consultant is myself, and I have a good instinct for this stuff.” Accepting the Republican nomination, he noted, “Nobody knows the system better than me, which is why I alone can fix it.” In the long run, however, the presidency has a way of humbling even the most self-assured. ...