As polls open for US primaries in Ohio and Florida, the political elite in Tokyo is starting to confront a disconcerting idea: that their indispensable US ally could actually elect Donald Trump as president.
The controversial businessman, now favorite for the Republican nomination, hits Japan regularly in his stump speeches for supposedly unfair trade practices and freeriding on US military protection.
According to a number of officials, Tokyo is still fairly relaxed about Mr Trump's views on security, regarding the US-Japan alliance as strong enough to cope, but they are becoming increasingly alarmed by bipartisan attacks on the Trans-Pacific Partnership, a trade deal crucial to Prime Minister Shinzo Abe.
"To start with they just thought 'he's funny'," said Masatoshi Honda, a professor of politics at Kinjo University. "But recently they're starting to worry — what happens if Trump wins?"
Like the political establishment in Washington, Tokyo has been slow to take Mr Trump seriously, not least because his rhetoric seems stuck in the 1980s, before Japan suffered two decades of economic stagnation and its population began to decline.