Kudos to President Trump for tweets tearing into China and President Xi Jinping on Friday for not stepping up to stop fentanyl shipments to the United States. With 47,600 opioid deaths in 2017 alone, this crisis must end.

The president should double down while sharpening and refining his messaging. And he should do so regardless of the ups and downs of tariff negotiations.

China has become the worldwide manufacturing hub of opioids, and with that has arisen criminal businesses that export fentanyl and other deadly narcotics to the United States. These businesses are sophisticated and slick: they operate through well-designed websites that include online chats, negotiate for bulk purchases, take bitcoin payments and even specify shipping preferences.

This was thoroughly documented in a January 2018 bipartisan report by the Investigations Subcommittee of the U.S. Senate’s Homeland Security and Government Affairs Committee. The report also found, “The preferred method of the international online sellers is Express Mail Service (EMS) … The EMS network delivers letters and packages through each member country’s postal operations.”

This is because since 2002, private express carriers can only accept packages that have advanced electronic data (AED) tracking information. With AED and advanced data analytics, suspicious packages are much more likely to be identified and seized.

In October 2018, the president signed the Synthetics Trafficking and Overdose Prevention (STOP) Act requiring that all inbound mail and packages from China have AED by Jan. 1, 2019. Yet, the law is currently in a weird no man’s land, with no penalty imposed for non-AED packages. Today, 15 percent of incoming postal items from China still do not have electronic tracking.

This means that special focus should be given to severing opioid shipments that come from China Post, China’s postal service and a government entity, through which most fentanyl and illicit opioids flow. The president should concentrate his future firepower on China Post. The Chinese delivery service is the aorta for fentanyl shipments to the U.S. and it must be clamped.

The president should order the Postal Service to return to China any packages that do not have electronic tracking. While the Postal Service appears hesitant to do this because of concerns about interruptions in legitimate commerce and potential retaliatory action from China, the president will show boldness and resolve by taking such action.

And, it is by no means a radical step. China already requires electronic tracking on all U.S. mail and packages going into China. In November, following U.S. enactment of the STOP Act, China’s General Administration of Customs, with dictatorial efficiency, enacted a similar electronic-tracking law to The STOP Act, but giving U.S. companies just three weeks to comply, which they have done.

Showing resolve on fentanyl shipments will also bolster the U.S. negotiating position for a new international shipping agreement for small packages at the Universal Postal Union (UPU).

This United Nations agency sets international mail prices and, through China’s influence, has institute a bizarre system which makes it less expensive to send a small package from Beijing to the United States than to send the same package domestically. This means tens of billions in lost U.S. business sales and U.S. job losses. The Administration simply wants to be able to charge foreign shippers the same as domestic customers pay for U.S. postal services.

There are other steps that must be undertaken to close the fentanyl pipeline from China. The budgets of U.S. Customs and Border Protection and the U.S. Postal Service’s Office of the Inspector General, which is involved in drug interdiction, should be strengthened. Congress should get on with the business of postal reform so that the U.S. Postal Inspection Service is ensured of having adequate resources.

We also need to demand that China arrest and send to the United States drug lords who have been and will be indicted. China must be persuaded to confiscate and shut down drug factories. And, we should have regular, high-level communications with China on these matters.

By taking these and other actions, we will save tens of thousands of American lives, and truly show China that we will no longer be pushed around.

Paul Steidler is a senior fellow with the Lexington Institute (@LexNextDC), a public-policy think tank based in Arlington, Virginia.