After 16 months of warm words, lavish gifts and rounds of golf, Prime Minister Shinzo Abe may be discovering the limits of personal rapport with U.S. President Donald Trump.

The prime minister is planning a hastily arranged trip to Washington next month after two surprise announcements by the U.S. president: That he'd meet their mutual adversary Kim Jong Un, and levy tariffs on Japanese steel and aluminum. The moves could shake the pillars of trade and security that underpin a 70-year-old alliance Abe was counting on to buttress against a rising China.

"The effect of a personal relationship is very uncertain," said Akihisa Nagashima, a former vice defense minister who is a lawmaker with Japan's opposition Kibo no To (Party of Hope). "This may even have been unrequited love."