All week long, news organizations chased down one Trump tall tale after another. PolitiFact, a website devoted to checking the veracity of claims by public officials, published 12 “of the most misleading claims” Mr. Trump made during his first White House interview. The Chicago Tribune found that Mr. Trump was incorrect when he claimed two people were shot and killed in Chicago the very hour President Barack Obama was there delivering his farewell address. (There were no shootings, police records showed.) The Philadelphia Inquirer found that Mr. Trump was incorrect when he said the city’s murder rate was “terribly increasing.” (The murder rate has steadily declined over the last decade.) The indefatigable fact checkers at The Washington Post cataloged 24 false or misleading statements made by the president during his first seven days in office.

But for students of Mr. Trump’s long business career, there was much about President Trump’s truth-mangling ways that was familiar: the mystifying false statements about seemingly trivial details, the rewriting of history to airbrush unwanted facts, the branding as liars those who point out his untruths, the deft conversion of demonstrably false claims into a semantic mush of unverifiable “beliefs.”

Mr. Trump’s falsehoods have long been viewed as a reflexive extension of his vanity, or as his method of compensating for deep-seated insecurities. But throughout his business career, Mr. Trump’s most noteworthy deceptions often did double duty, serving not just his ego but also important strategic goals. Mr. Trump’s habitually inflated claims about his wealth, for example, fed his self-proclaimed image of a business genius even as they attracted lucrative licensing deals built around the Trump brand.

Nearly 30 years ago, in his best-selling book “The Art of the Deal,” Mr. Trump memorably extolled the advantages of “truthful hyperbole,” which he described as “an innocent form of exaggeration — and a very effective form of promotion.” It is one thing when the hyperbole comes from a reality TV star exaggerating his ratings to a roomful of television critics. The stakes are infinitely higher when it comes from the leader of the free world, and this reality is provoking alarm from many across the political spectrum.