WASHINGTON — Donald J. Trump lost an auction in 1988 for a 58-key piano used in the classic film “Casablanca” to a Japanese trading company representing a collector. While he brushed off being outbid, it was a firsthand reminder of Japan’s growing wealth, and the following year, Mr. Trump went on television to call for a 15 percent to 20 percent tax on imports from Japan.

“I believe very strongly in tariffs,” Mr. Trump, at the time a Manhattan real estate developer with fledgling political instincts, told the journalist Diane Sawyer, before criticizing Japan, West Germany, Saudi Arabia and South Korea for their trade practices. “America is being ripped off,” he said. “We’re a debtor nation, and we have to tax, we have to tariff, we have to protect this country.”

Thirty years later, few issues have defined Mr. Trump’s presidency more than his love for tariffs — and on few issues has he been more unswerving. Allies and historians say that love is rooted in Mr. Trump’s experience as a businessman in the 1980s with the people and money of Japan, then perceived as a mortal threat to America’s economic pre-eminence.

“This is something that has been stuck in his craw since the ’80s,” said Dan DiMicco, a former steel executive who helped draft Mr. Trump’s trade policy on the 2016 campaign trail and in his presidential transition. “It came from his very own core belief.”

The affection has grown in recent years, as tariffs have emerged as perhaps the most potent unilateral tool that Mr. Trump can wield to advance his economic agenda — and perhaps the purest policy expression of the campaign themes that lifted him to the White House.

“Tariffs tie so much of Trump together, ” said Jennifer M. Miller, an assistant history professor at Dartmouth College who last year published a study of how Japan’s rise has affected the president’s worldview. “His obsession with winning, which he thinks tariffs will allow him to do. His obsession with appearing tough. His obsession with making certain parts of national border fixed. And his obsession with executive power.”