Given this, no single country has the power to force China to reform its ways, the thinking goes. China can get around tariffs in one nation by sending its wares elsewhere. It can buy its way into markets by wielding its largess, building infrastructure and proffering loans.

Most experts assume that the only way to make progress in pressuring China to play fair is through collective action. Major economies must join forces, taking cases at the World Trade Organization and harmonizing their policies.

“There are some grave concerns on China, who are massively subsidizing state-owned companies,” the European Union trade minister, Cecilia Malmstrom, said in January, on the sidelines of the World Economic Forum in Davos, Switzerland. “And there, yes, we could work with the U.S.”

Yet Mr. Trump is pursuing the opposite course.

In one of his first acts as president, he renounced American participation in the Trans-Pacific Partnership, a trade bloc forged by the Obama administration in part as a counter to China’s rise. The pact included prohibitions on state subsidies, in what was supposed to be a template that could eventually influence China’s commercial realities.

Mr. Trump has also attacked the World Trade Organization — the linchpin of the global trading system and the ultimate venue for collective action — even suggesting that he might revoke American participation. In a formal statement to a congressional committee on Wednesday, a top White House trade official called the W.T.O. “wholly inadequate to deal with China’s version of a state-dominated economy that rejects market principles.”

Mr. Trump has, at least for now, exempted Canada and Mexico from the bite of his tariffs on steel and aluminum. But that is conditional on their satisfying his demands for sweetened terms in the renegotiation of the North American Free Trade Agreement.