President Donald Trump's five-nation Asia trip got off to a low-key start Sunday as he enjoyed a round of golf with Japanese Prime Minister Shinzo Abe.

The two leaders hit the links not long after a lunch of American-beef hamburgers, not long after Trump's arrival from Hawaii.

But the display of friendship from Abe will soon give way to high-stakes diplomacy. Still, the two men have struck up an easy rapport.

Their formal talks are set to begin Monday in Tokyo. Abe will be looking for a united front against North Korea and reassurances that the U.S. will stand by its treaty obligations to defend Japan if falls under attack.

Eager to forge a bond with Tokyo's crucial ally, Abe was one of the first world leaders to court President-elect Trump. He was the first to call Trump after the election, and rushed to New York days later to meet the president-elect and present him with a pricey, gold Honma golf driver.

The two men also met on the sidelines of an international summit in Italy this spring and White House officials said Trump has spoken with Abe by phone more than any world leader, aside from British Prime Minister Theresa May.

That bond was clear Sunday, as Trump and Abe exchanged glowing tweets about their game. Trump dubbed Abe and pro golfer Hideki Matsuyama -- who accompanied the two leaders -- as "wonderful people," while Abe called it a "round of golf with a marvelous friend."

From the time Marine One landed on the Kasumigaseki Country Club's driving range, Abe rolled out little touches to make Trump feel welcome. He presented a hat that had a version of Trump's campaign theme, this time reading "Donald and Shinzo: Make Alliance Even Greater."

The two passed up the region's famed Kobe beef in favor of the American version, which is favored by Trump, a famed picky eater.

When Trump hosted Abe in Palm Beach, Fla., earlier this year, they played at one of Trump's golf courses. For that outing, Trump brought along pro golfer Ernie Els, so this time Abe matched him by bringing along Matsuyama, whom Trump described on the plane ride to Asia as "probably the greatest player in the history of Japan."

Abe was behind the wheel of a golf cart as the two men were spotted moving from hole to hole, Trump in the passenger seat smiling and waving at those they passed.



"From the point of view of Abe administration, the personal chemistry that exists between the two leaders is seen as an asset," said Mireya Sollis, chair in Japan Studies for the Brookings Center for East Asia Policy Studies.

She said that the Japanese believe it is already "seeing it pay off," including when Trump agreed to meet with the families of Japanese citizens kidnapped by the North Korean regime, an important issue for Tokyo.

Ever since Saudi Arabia delivered a lavish welcome on Trump's first international trip, leaders have tried to outdo themselves to impress the president, who has proven susceptible to flattery.

Before the game, Trump delivered a speech in which he hailed Japan as a "crucial ally" and warned adversaries not to test America's resolve.

"Japan is a treasured partner and crucial ally of the United States and today we thank them for welcoming us and for decades of wonderful friendship between our two nations," Trump told American service members at Yokota Air Base on the outskirts of Tokyo.

Though Trump did not mention North Korea by name during the speech, the spectre of its weapons program will loom large throughout Trump's five-nation Asia trip. The president warned of the consequences of crossing what he called the "most fearsome fighting force in the history of our world."

"Together with our allies, America's warriors are prepared to defend our nation using the full range of our unmatched capabilities. No one -- no dictator, no regime and no nation -- should underestimate, ever, American resolve," he told the troops.

And while there is worry in the region about Trump's unpredictable response to the threat posed by Kim Jong Un, Trump made clear he did not intend to tone down his bellicose rhetoric -- which included dubbing Kim Jong Un as "Little Rocket Man" -- even while in an Asian capital within reach of the North Korea dictator's missiles.

"There's been 25 years of total weakness, so we are taking a very much different approach" in dealing with the renegade regime in Pyongyang, he said, speaking to reporters on Air Force One.

Trump also said it is "expected" that he'll meet with Russian President Vladimir Putin on the sidelines of an upcoming summit in Vietnam.

The easy rapport with Japan could be strained if Trump takes an aggressive approach on trade or the two men disagree on the need for a diplomatic approach to the threat looming in Pyongyang.

During his campaign, Trump suggested Japan should acquire its own nuclear weapons to defend itself, hinted the U.S. might not come to the nation's defense, and accused Japan of "killing us" on trade. He has dropped that antagonist language almost entirely since the election, but tensions remain.

Japan was a chief proponent of the Trans Pacific Partnership, a trade deal Trump pulled out of.

Scott Seaman, a director for Asia of the Eurasia Group, a political risk consultant organization, noted: "everything is fine with Trump until you tell him no. So far, Abe hasn't told him no."

The Associated Press contributed to this story.