Forget tariffs. Forget all the computers, toys and textiles that the Chinese export to America.

China’s most consequential export here is fentanyl, the illicit drug killing people in this country at the rate of nearly 80 a day.

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Fentanyl use in the USA has surged, pushing its death toll last year to 28,466  — nine times higher than in 2013 and a rise so steep that it has helped drive down the nation’s life expectancy.

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And where is this illicit fentanyl originating?

About 80 percent of the pure fentanyl seized by U.S. authorities last fiscal year arrived from China, often through the mail.

Since the recent summit in Argentina of the Group of 20 industrial and emerging-market nations, President Donald Trump has boasted on Twitter that Chinese President Xi Jinping agreed to “criminalize the sale of deadly fentanyl” coming into the United States, a potential “game changer” in the battle against this mass killer.

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Trump didn’t get it quite right. Fentanyl already is an illegal “controlled substance” in China. The Chinese Foreign Ministry said last week that it would add “all fentanyl-like substances” to its controlled substance list — a change that could be quite far-reaching. At the same time, China cautioned patience: “The relevant work is yet to be started.”

Fentanyl is a particularly insidious killer. It’s far more potent than heroin and more profitable for dealers because a kilo can be cut into so many more doses. It is often laced into heroin or pressed into fake pain pills by sellers who care nothing about accuracy, so users don’t know what they’re getting. Tiny variations in dosages can be fatal.

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The drug’s structure is also a problem. Unlike heroin, which is made from poppies grown in fields, fentanyl is a synthetic drug manufactured in laboratories. Once China declares one form a “controlled substance,” chemists can tweak the core formula by as little as a single molecule and create what’s known as a new “analogue” that is not yet illegal. That leaves U.S. law enforcement one step behind the criminal traffickers.

If China declared all fentanyl-like substances illegal, it could deeply cut into exports.

Regardless of China’s intentions, there are built-in barriers to curtailing fentanyl exports. Chinese regulators are understaffed and overwhelmed by the nation’s enormous chemical and pharmaceutical industries.

And while the national government sets policy, it is carried out locally, where officials could be more interested in boosting the economy than curbing a drug that the Chinese maintain is not abused in their own country.

The history of follow-through on crackdown promises is mixed. In 2015, after a new Chinese drug known on the street as flakka caused dozens of deaths in Florida, U.S. officials were able to quickly get China’s cooperation in declaring the drug a “controlled substance.” It soon disappeared from Florida.

But even as the United States has waged a long campaign against fentanyl imports, including new postal requirements for international mail, the drug’s flow and resulting deaths have surged. In the past 14 months, federal prosecutors have indicted several Chinese nationals for selling fentanyl to Americans over the internet, but neither the Chinese nor the U.S. Justice Department would say whether any have been arrested in China or have had their labs shut down.

Whether Trump’s meeting with Xi results in meaningful progress remains an open question. The only thing certain is that every day this poison continues flowing into American communities, more people will die.

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