WASHINGTON ― Sen. Rob Portman (R-Ohio) sees President Donald Trump’s Thursday meeting with Chinese President Xi Jinping as an opportunity to address a key driver of the opioid epidemic. Portman encouraged the president to confront the Chinese leader about his country’s manufacturing of synthetic opioids like fentanyl.

Portman, in a letter to Trump, argued that the roots of the deadly crisis don’t just come from Mexican heroin traffickers and Big Pharma’s painkillers, but also from Chinese manufacturers shipping deadly synthetic opioids that have infiltrated the black market.

“U.S. law enforcement agencies report that the majority of fentanyl found in the illegal drug market is produced in China,” Portman wrote. “Law enforcement has detected efforts by drug traffickers to smuggle fentanyl across both the Northern border from Canada and the Southwest border from Mexico. However, increasingly fentanyl comes into the United States directly from China by express and traditional mail. Chemical testing of fentanyl seized by law enforcement from the United States Postal Service, as well as from private or express consignment shipping companies (UPS, DHL, FedEx) suggest that the fentanyl coming by direct shipments is deadly, with a purity of higher than 90 percent.”

Law enforcement and public health officials have struggled to curb the opioid epidemic for years. The influx of fentanyl represents a significant escalation in the crisis. It is more potent than prescription painkillers and heroin, and has led to fatal overdose deaths across the U.S. Portman’s letter noted the latest grim statistics tallied by the Centers for Disease Control and Prevention.

Deaths involving fentanyl and synthetic opioids rose to 9,580 in 2015, an increase of 73 percent over the previous year, Portman wrote. “Fentanyl is 30 to 50 times stronger than heroin and often emerges in the illegal drug market laced with powder heroin or pressed into tablets designed to mimic the appearance of a prescription opioid,” he added.

Portman noted that Trump addressed the issue during the presidential campaign and supported his bill aimed at stopping the flow of opioids. The senator even quoted the president to make his point, noting that Trump promised to “close the shipping loopholes that China and others are exploiting” and vowed to “crack down on this abuse, and give law enforcement the tools they need to accomplish this mission.”

Last week, Trump announced a new commission to examine the opioid epidemic and identify ways the federal government could address it. In a roundtable discussion on the issue, Chinese synthetic opioids came up briefly, but Trump did not mention China or his upcoming meeting with Xi.

Trump was asked more broadly about the opioid epidemic, and whether “he would take this issue on the road,” according to the media pool report of the roundtable.

“Yes we will,” he said. “Big issue. Very, very big issue.”