LONDON — As President Trump intermittently escalates and moderates his trade war with China, his conflicting signals reflect a reality that limits his actions: He can try to sever the deeply intertwined American commercial relationship with China, or he can prod economic growth to assuage the fears of investors around the planet.
But he cannot do both at the same time.
Mr. Trump need not rely on the testimonials of economists to deduce this. He can disregard the admonitions of news outlets he derides as fake news. He can simply consult the one source whose verdicts he tends to celebrate: the stock market.
Among those who control money, portents of further trade hostilities between the United States and China, the two largest economies on earth, have proved an impetus to sell with abandon while amplifying talk of recession. Intimations of a deal avoiding further animosity reverberate as a clarion call to buy, sending share prices higher while easing worries about a potential global economic downturn.
Mr. Trump often appears caught between competing impulses that pull markets — and his China policy — in opposite directions.
Talk of a trade deal with China makes for happy stock markets and retirement account statements that Americans open up to learn that they are, also happily, richer. For a president seeking re-election next year, this option holds appeal.
Thunderous threats of fresh tariffs on Chinese goods and the forging of a new order in which American industry forsakes China may damage share prices and shrink economic growth prospects. But it brings plaudits from Mr. Trump’s most ardent political base — nationalists who portray the trade war as a tough but necessary piece of business, the sort of action evaded by the cowards who resided at the White House before.
The latest evidence for this state of affairs came in recent days, as Mr. Trump angrily reacted to China’s announcement of retaliatory tariffs of 10 percent on some $75 billion worth of American exports.
On Friday, the president unleashed furious tweets threatening China with pain. He vowed to raise tariffs on $550 billion of Chinese goods. He declared that China’s president, Xi Jinping, whom he had previously called a “good man,” was an “enemy.” And he commanded American companies to abandon China and start making their products in the United States.
That last bit was especially striking given that successive American administrations have criticized Chinese counterparts for using state-owned companies as tools of policy in contravention of market forces. Now, here was the president of the United States, traditional champion of swashbuckling capitalism, ordering American companies to heed his dictates.
In markets around the globe, investors reacted to these developments as powerful signals to yank their money to safety. They sold stocks and bought bonds. They dumped a vast assortment of currencies and purchased the American dollar, the ultimate haven in moments of worry.
They reacted, in short, as if much of the globe suddenly appeared riskier.
Signs of trouble had already been mounting. For better or worse, the United States and China have been fused for two decades, with their fortunes influencing economic conditions everywhere.
China has invested aggressively in manufacturing plants, ports and power systems to become the factory to the world. American consumers are the most significant drivers of economic growth on earth. Together, the United States and China are responsible for about 40 percent of the world’s economic output.
Any sign of a breakdown in this arrangement — the threat that China will be impeded in selling its goods, or that the American appetite is waning — spreads worry far and wide.
The trade war that has escalated over the last year has already produced distress. Germany, the largest economy in Europe, is teetering toward recession in large part because of weakening exports. As China’s economy slows in the face of American tariffs, Chinese factories have less need for goods made in Germany, from machinery to petrochemicals.
German weakness has contributed to a general sense of malaise in Europe, just as the Continent grapples with the prospect that Britain — also contracting — might crash out of the European Union without a deal governing future commercial relations.
Across Asia, the drop in trade has sown trouble, with Singapore and Hong Kong now declining and South Korea slowing. Even Vietnam — a country that has received fresh investment as multinational companies seek alternatives to making their wares in China — looks vulnerable if global trade over all continues to diminish.
As far away as Brazil and Argentina, the impacts of a slower-growing China are being felt by soybean farmers who ship their harvest to Chinese ports to feed livestock.
“For the rest of the world, there are many other countries that are innocent bystanders that will actually suffer even more than the United States and China,” said Louis Kuijs, the Hong Kong-based head of Asia economics at Oxford Economics. “There is not going to be any de-escalation any time soon.”
“对于世界其他地区来说，许多国家都是无辜的旁观者，它们遭受的损失将超过美国和中国，”常驻香港的牛津经济咨询社（Oxford Economics）亚洲经济主管高路易（Louis Kuijs）说。“短期内不会出现缓和。”
Beijing and Washington have argued over this state of affairs for decades, while American labor interests and industry groups have demanded redress.
But Mr. Trump has gone much further than his predecessors in his diagnosis. In his telling — at least, in his combative moments — China is a rogue operator that fleeces Americans. The solution is not another slow-moving case at the World Trade Organization, but a fundamental redrawing of commercial geography. American companies must vacate China, walking away from customers and supply chains. In his view, the American economy is supposed to “decouple” from China, as the think tank vernacular has it.
Mr. Trump’s tweet storm on Friday morning appeared to underscore that he was serious, that he was truly willing to see Americans accept the costs — plunging stock markets, weakening investment — for a wholly new sort of relationship with China as adversary.
Stock markets suffered a sell-off because a dissolution of American and Chinese commercial arrangements was certain to be disruptive. Companies with global operations would have to scramble to figure out where they would buy parts and raw materials. The potential outcomes were many, but none of them involved the world’s getting richer.
Yet by Sunday morning, at the Group of 7 summit in France, Mr. Trump was expressing “second thoughts” about the new tariffs on Chinese goods. By Monday morning, he was calling Mr. Xi a “great leader” and reporting that China was interested in resuming trade talks. Stock markets were buoyant. At least for a few hours, the bewildering notion that the United States and China were dissolving ties could be forgotten.
But for how long? And what is the end game?
For as long as Mr. Trump has occupied the Oval Office, trade experts have parsed his often contradictory words and actions for clues to his real policy aims and beliefs. They have labored to divine what he values, and somehow separate it from what he may say as a negotiating ploy or as a diversion from scandal.
Trump is famously adept at maintaining positions that seem mutually exclusive. In recent weeks, he has touted the awesome strength of the American economy while excoriating the Federal Reserve chair for imperiling the economy by not aggressively lowering interest rates. He has flirted with tax breaks to juice the economy further.
But the trade war threatens to force Mr. Trump to choose between it and economic growth.
In Beijing and Washington alike, hard-liners have dug in, shrinking room for a compromise. In both capitals, a sense of permanent alteration has transpired, a deepening assumption that — whatever comes next — China and the United States will proceed with profound wariness.
For the global economy, that could entail grave uncertainties and perils.