The titans of finance who gathered on Thursday at the Economic Club of New York may have hoped to hear how former President Donald J. Trump would take the nation into the era of artificial intelligence, private space travel and self-driving electric cars.

Instead, they were treated to an extended discourse on the glories of William McKinley and the power of tariffs to cure all that ails what Mr. Trump called a nation nearing economic collapse. Rather than new policies for the 21st century, the former president often harked back to the end of another century, the 19th.

“In the words of a great but highly underrated president, William McKinley, highly underrated, the protective tariff policy of the Republicans has been made — and made — the lives of our countrymen sweeter and brighter,” he said on Thursday during a rambling speech billed as a major economic address.

Mr. Trump seemed aware that his prescriptions for import tariffs on every product made abroad and a preferential 15 percent corporate tax rate for domestic manufacturers might not resonate in the high temple of global finance.

“You can call it what you want; some might say it’s economic nationalism,” he said after name-checking some of Wall Street’s richest men, such as Stephen A. Schwarzman, the chief executive of the Blackstone Group, Jamie Dimon, the chief executive of JPMorgan Chase, and John Paulson, the famed hedge fund manager. “I call it common sense. I call it America First. This is the policy that built this country, and this is the policy that will save our country.”

His solution for the deficit? Tariffs. The crisis for middle-class families struggling with child care? The economic growth he said would be spurred by things like tariffs. A complicated international supply chain that has the wings of military aircraft manufactured in one country and the tail in another? Tariffs.