President Trump and Japanese Prime Minister Shinzo Abe were all smiles Sunday as they replaced tough tariff talk with personal diplomacy, enjoying a round of golf in Chiba on Sunday and taking in a sumo wrestling tournament in Tokyo.

Japanese Prime Minister Shinzo Abe’s fun-filled weekend appeared to be paying off, at least on the surface. He posted a selfie of the leaders smiling on the golf course, while Mr. Trump said the toughest trade talks will take place after Japanese elections.

“Great progress being made in our Trade Negotiations with Japan. Agriculture and beef heavily in play. Much will wait until after their July elections where I anticipate big numbers!” Mr. Trump said on Twitter.

Mr. Abe’s charm offensive during the three-day trip is aimed at shoring up his warm relationship with Mr. Trump, while keeping the threat of debilitating U.S. tariffs on Japanese autos out of the headlines before the looming elections.

While the men golfed, First Lady Melania Trump and Mr. Abe’s wife, Akie Abe, visited the teamLab Borderless museum in Tokyo, an innovative collection of digital exhibits.

Later, the first couple took in a sumo wrestling tournament at Ryōgoku Kokugikan Stadium. They were seated in chairs — not on the traditional mats — a few yards from the sumo ring, and Mr. Abe appeared to lean over and describe the action at times.

Reporters traveling with the president said he did not appear to clap or react much when the wrestlers faced him, threw ceremonial salt or swayed from side to side.

Capping the tournament, Mr. Trump emerged with the “President’s Cup,” eliciting oohs and ahhh from the crowd. He read a “certificate of commemoration” for Asanoyama, the winner, and presented the trophy.

“In honor of your outstanding achievement as sumo grand champion I hereby award you the President’s Cup,” Mr. Trump said.

He read aloud the date under the Japanese era called “Reiwa,” in recognition of the ascension of the new emperor.

Mr. Trump and the first lady then had a postgame meal at Inakaya, a hibachi restaurant.

Though he was thousands of miles away, Mr. Trump’s ongoing political feuds remained front and center during the trip. At one point, he dragged the Japanese into the spat.

“Numerous Japanese officials told me that the Democrats would rather see the United States fail than see me or the Republican Party succeed - Death Wish!” he said on Twitter.

Mr. Trump and Mr. Abe are expected to discuss military cooperation Monday, as North Korea’s missile program and nuclear ambitions remain a major issue in the region.

Mr. Trump appeared to contradict his national security adviser, John Bolton, who on Saturday said recent North Korean missile tests violated U.N. Security Council resolutions.

“North Korea fired off some small weapons, which disturbed some of my people, and others, but not me,” he tweeted, before taking a swipe at his most prominent 2020 Democratic rival. “I have confidence that Chairman Kim will keep his promise to me, & also smiled when he called Swampman Joe Biden a low IQ individual, & worse. Perhaps that’s sending me a signal?”

The tweet was corrected from an earlier version that misspelled Mr. Biden’s last name as “Bidan.”