China's leaders are tormented by the "Malacca Dilemma". Their country is the world's largest importer of oil and natural gas. It is acutely vulnerable to an energy squeeze on seaborne supplies.
More than 82pc of China's total crude shipments and much of its liquefied natural gas passes through the Malacca Strait between Sumatra and the Malay Peninsular. The US navy has supremacy over this maritime choke-point, though not necessarily for long.
Energy security has long been a nagging worry among China's defence strategists. They have studied the Royal Navy's "limited blockade" of the Falkland Islands in 1982 as the modern textbook case of how maritime powers can tighten their grip.
The issue became all too real last week when Fu Chengyu, ex-head of the state oil giant Sinopec, said the country must prepare for the awful possibility of a US oil blockade.
"It is not to be alarmist. It is an urgent reality," he told a forum in Shanghai. China's strategic petroleum reserve will not be complete before the early 2020s.
State media says stocks are barely enough for 40 days usage - Platts analysts think Japan can last 222.The Malacca Dilemma is a metaphorical term.
The US would first try to achieve its objectives through control over the world's dollarised payment and lending system. Even so, a commodity squeeze would entail a worldwide recessionary shock and an economic crunch in the US oil patch.
"It would cause the price of West Texas crude to crater. The Trump administration has absolutely no interest in doing that," said Ian Bremmer from Eurasia Group, the political risk firm." Trump has already rattled the cage with Huawei. This is all about technology, not resources - and the one place where China really is vulnerable is on semiconductors."
There are two tech superpowers out there that can't be reconciled. Countries like Britain are going to have to choose one," he said. Yet the Chinese leadership has brought the Malacca Dilemma into sharp focus by threatening - through state-controlled media - to restrict exports of rare earth minerals. This would purportedly cut off the life-blood of the US technology industry.
Yet it is a high-risk gamble. The more that Beijing plays the commodity card, the greater the risk Donald Trump will play it back, with interest.
What is clear is that the Sino-US trade war is taking a dangerous turn. Trump may have pushed China too far in demanding changes to the country's domestic law and a unilateral enforcement mechanism. This smacks of the "unequal treaties" imposed on the Qing dynasty in the 19th century.
China is drawing up its own "unreliable entity list" to fight back against the US suffocation of Huawei.
Google, Intel and Qualcomm will almost certainly be on it, since they have begun halting critical dealings with Huawei. British firms may be caught up in the sweep. Any foreign executive or employee working for these entities could be prevented from leaving the country or face arrest on dubious charges.
This has already happened to two Canadian citizens detained on espionage charges, deemed in Ottawa to be blatant hostage-taking. "If I were still living in China with my family I would be far along with my exit plan and ready to execute it at very short notice," said Bill Bishop of Sinocism.
Bishop said the People's Daily has pointedly revived an expression with powerful symbolism in Chinese revolutionary history: "Don't say I didn't warn you".
It was used in the Sixties when Mao Zedong's China attacked a Soviet border post, almost precipitating a third world war. The Soviet Union had earlier cut off oil supplies to China, causing drastic rationing. That trauma is not forgotten. The term was also invoked just before frontier wars with India and Vietnam.
The episodes are known in China as the "three self-defence counter-attacks".
While the quarrel with America has not reached such a combustible stage, it could escalate fast if the US Congress presses ahead with a bill mandating sanctions over the alleged incarceration of 1m Muslim Uighurs from Xinjiang in political re-education camps.Laban Yu from Jefferies says the Chinese leadership is afraid that the US could try to quarantine the country.
"China is now looking at its oil supply situation from the worst-case scenario, like what the US has done to Iran," he told Bloomberg.
Sinopec's Fu Chengyu said China must accelerate the switch to electric vehicles, double down on domestic "clean" coal and launch shale gas fracking in Xinjiang and Sichuan on a vastly expanded scale with cheap credit. This would not come soon enough to make any difference in the current trade war. China's leaders know what happened to Japan in 1940 when President Franklin Roosevelt began to restrict oil export permits for the Tojo regime. It set off a spiral that led ineluctably to the Pacific war.
The Malacca Dilemma renders China's rare earth weapon dangerously double-edged. The minerals are certainly a potent tool. China not only mines 80 per cent of world production, it has near total control of the global processing chain. Beijing has systematically pressured foreign companies into locating facilities in China to secure rare earth supplies.
Whole components of US manufacturing - car starters or aircraft parts - are pre-finished there before shipping to America.
The US General Accounting Office says it would take seven to 15 years to set up a parallel supply structure."They know our supply-chains. They can target industries," said Clint Cox, a rare earth expert at Anchor House. "Basically, anything that moves in your car has rare earths in it. Most of our companies don't have significant inventories," he said.
The metals are critical for smart bombs, precision-guided missiles, lasers, submarine sonar and the F-35 joint strike fighter.
"They are used in everything but bullets," said James Kennedy of ThREE Consulting. Yet China cannot embargo the US without disrupting the world's inter-twined supply chain and hurting everybody else. When Beijing cut off rare earth supply to squeeze Japan over the Senkaku Islands in 2010, the price of lanthanum (a catalyst in oil refineries) rose 30-fold in panic buying.
To play this card would cut across Beijing's other goal: to stake out the moral high ground in its dispute with Trump and displace Washington as the arbiter of 21st century globalisation. Yet President Xi Jinping undoubtedly issued a veiled threat in late May when he combined a pilgrimage to the Jiangxi shrine of the Long March with a tour of a rare earth magnet factory.
The elemental problem for Xi is that Washington could bring the Chinese economy to its knees by commodity strangulation before China's rare earth blockade had seriously crippling effects on the US. He can try to ratchet up the pressure with a -carefully calibrated constriction of rare earth components, but if he pushes too hard against the volatile US president, he risks exposing the hard truth that the leverage of the two countries is not symmetric.
Whoever you are, you must always assume Donald Trump might out-escalate you.