Chinese strongman Xi Jinping has a terrible weakness - and his name is Kim Jong Un.
This is supposed to be the Chinese President's big moment. Not since Deng Xiaoping's day has a mainland leader controlled, well, everything - foreign affairs, the economy, the military, censorship policy, you name it.
United States President Donald Trump's erratic White House and his scrapping of trade and climate-change deals, meanwhile, makes Mr Xi's team look like the adults in the room.
Except for that Kim fellow, whose antics in Pyongyang have strongman Xi looking befuddled and downright cowed. Mr Xi had better get his mojo back, and soon, to curb the North Korean leader's provocations the way only he can.
Increasingly, Beijing's global standing depends on it.
The US President is turning up the pressure on Mr Xi to get tough on his client-state. Mr Trump is inching towards blunt force, too, be it military action on the Korean peninsula or a trade war with China. But greater success might come from pulling Japan into the mix to throw Mr Xi off balance and prod him to use Beijing's considerable leverage over Mr Kim.
Japanese Prime Minister Shinzo Abe could do just that by urging the US to install a web of Terminal High Altitude Area Defence (Thaad) systems around his geopolitically vital nation. Mr Abe also could host America's Aegis Ashore weapons-interception system, which his defence team recently visited Guam to investigate.
China reacted angrily when South Korea welcomed Thaad onto the peninsula, banning tour groups, turning away K-pop bands and shuttering Lotte stores. Imagine the shockwaves through Beijing's halls of power if Japan followed suit - and the changes to Mr Xi's North Korean calculus.
Tokyo already has a two-step missile-defence programme. But given Mr Kim's leaps in intercontinental ballistic missile (ICBM) technology, reinforcements are in order. That would surely clarify Mr Xi's thoughts on the need to dock Mr Kim's allowance.
The missile-shield hardware is only one half the problem for Mr Xi. The other is considerably more US radar and surveillance technology in China's backyard. Few steps would shake up the status quo in North Asia, and more quickly.
What could Mr Xi do?
Mr Kim giving up his nuclear warheads is a non-starter. He's well aware that Saddam Hussein and Muammar Gaddafi might still be alive and in power if they'd had nuclear deterrence.
But Mr Trump and Mr Abe are right that China has never tried seriously to tighten the financial screws. Sure, Mr Xi supports the occasional United Nations sanctions. In February, Beijing temporarily banned coal imports after Mr Kim's half-brother was assassinated. Mr Xi has treaded carefully, though, concerned about destabilising the Kim regime and risking a refugee crisis on China's border with the North.
It's time Mr Xi experimented.
Mr Kim gets 90 per cent of his energy from China, which also supplied him with US$100 million (S$137 million) of steel last year. Why not send word to Pyongyang that Beijing is halving those shipments, effective immediately? The same goes for food, to say nothing of limiting Mr Kim's financial pipelines.
And then there's the Dandong problem. Mr Trump and Mr Abe favour so-called secondary sanctions against Chinese firms that run factories in this and other border cities. That would work only if Mr Xi clamped down on these specific trade flows. At the moment, they're working in a huge way for Mr Kim. Last year, his economy grew 3.9 per cent, the fastest in 17 years. Since Mr Trump took office in January, North Korea-China trade has swelled nearly 11 per cent. Figures like this give UN efforts a bad name and bolster Mr Trump's instinct that China isn't doing enough.
As Council on Foreign Relations president Richard Haas sees it, China is key to "put a ceiling" on Mr Kim's nuclear ambitions. The question, of course, is how to get China onboard. A good cop/bad cop routine may be just the thing.
South Korean President Moon Jae In wants to engage Mr Kim, resurrecting the 1998-2008 "Sunshine Policy". Diplomacy, as former US ambassador to the UN Bill Richardson says, must accompany whatever Mr Trump and Mr Abe have in mind. As Mr Moon passes out the carrots, Mr Abe can help the US with the sticks.
The risk of military action is too great to contemplate - millions of casualties on the Korean peninsula alone. Japan, a vital US ally that's an easier ICBM shot than San Francisco, is in harm's way. So is much of the Asian region, says Philippine President Rodrigo Duterte. While calling him a "fool", Mr Duterte said of Mr Kim, "if he commits a mistake, the Far East will become an arid land. It must be stopped, this nuclear war". Still, Mr Trump is warning Mr Kim it's a live option.
Japan's Thaad gambit is a wiser way to get Mr Xi, and Beijing's sizeable leverage, on the case. Mr Abe's Liberal Democratic Party has resisted the step, fearing Beijing would retaliate against Japan Inc. Somehow, though, the "lost trade with China" argument loses sway when an existential threat is rising just 1,284km from Tokyo.
Mr Xi talks of making China a bigger stakeholder in global affairs, not just a shareholder. There's no better way for him to prove it than taming Mr Kim.
If Mr Trump's bluster doesn't convince Mr Xi the time is now, perhaps a change in archenemy Japan's missile-deterrence policy will.
•The writer, a Tokyo-based journalist, is a former columnist for Bloomberg and author of Japanisation: What The World Can Learn From Japan's Lost Decades.