During the first administration of Donald J. Trump, if any world leader could claim to have had the now president-elect’s number, it was Shinzo Abe, Japan’s prime minister at the time.

Mr. Abe, who was assassinated by a gunman in 2022, was considered a Trump whisperer par excellence, tapping into the president’s love of golf, hamburgers and adulation in a way that helped shelter Japan from Mr. Trump’s punishing instincts.

Mr. Abe was the first foreign leader to visit Mr. Trump after he was elected in 2016, bringing a gift of golf clubs to Trump Tower in Manhattan. After the president’s inauguration, Mr. Abe quickly assumed the role of elder statesman guiding the new man on the world stage. On multiple phone calls, he was a reliable friendly ear. The first time Mr. Abe visited the new president at his plush resort residence, Mar-a-Lago, just weeks after Mr. Trump took office, the pair played golf together and dined with their wives.

When Mr. Trump came to Japan on a state visit, Mr. Abe piled on the pomp and circumstance, naming a trophy after the president to award at a sumo wrestling tournament and granting the American president the honor of being the first international leader to meet the newly enthroned emperor.

Mr. Abe “moved quickly enough, he got the tone right, he knew how to talk to” President Trump, said Tobias Harris, founder and principal of Japan Foresight, a risk consultancy in Washington. “It’s hard to think of a leader who did quite as well.”

Now, as Japan and the rest of the world brace for the next Trump administration, the question of how to manage the most mercurial of American presidents has officials frantically reviewing their playbooks from those first four years.