Air Force Gen. Glen VanHerck, commander of North American Aerospace Defense Command and U.S. Northern Command, presents a challenge coin Feb. 7, 2022, to Sgt. David Ewald of the Missouri National Guard’s 3175th Chemical Company during his deployment to McAllen, Texas. NORTHCOM is providing mobile surveillance camera operators, intelligence analysts, and aviation support operations to the Department of Homeland Security and U.S. Customs and Border Protection to help secure the southern border of the United States. (Lerone Simmons/U.S. Army)

A top Pentagon official told lawmakers Wednesday that she was wary of growing calls to deploy American troops into Mexico to battle cartels responsible for at least some of the deadly drugs pouring into the United States across the southern border.

Melissa Dalton, the assistant secretary of defense for homeland defense and hemispheric affairs, told House Armed Services Committee members that the Pentagon has found increasing violence in Mexico and the flow of the synthetic opioid fentanyl into the United States “deeply concerning.”

But Dalton also warned unilateral U.S. military action into Mexico could harm the relationship between the U.S. and its southern neighbor, after lawmakers in both chambers this year have raised the idea of designating some cartels as terrorist groups and sending U.S. troops into Mexico to confront them.

“In terms of weighing the advantages and disadvantages of some of the steps that are under consideration in terms of use of force or certain designations, I think we need to be clear-eyed about what some of the implications might be for the lines of cooperation we do have with Mexico,” Dalton said in response to an inquiry from Rep. Jimmy Panetta, D-Calif. “I do worry, based on signals — very strong signals we've gotten from the Mexicans in the past, concerns about their sovereignty, concerns about potential reciprocal steps that they might take to cut off our access, if we were to take some of these steps that are in consideration.”

Recent calls to deploy U.S. forces alongside U.S. law enforcement into Mexico to deal with the drug cartels have largely come from Republicans. In an op-ed published last week by The Wall Street Journal, former Attorney General Bill Barr, who served in that role under former presidents Donald Trump and George H.W. Bush, called for “a far more aggressive American effort inside Mexico than ever before.” He called on President Joe Biden to deploy “select military capabilities” into Mexican regions dominated by the cartels and endorsed a resolution proposed in January by Reps. Dan Crenshaw, R-Texas, and Michael Waltz, R-Fla., to provide presidential authority to battle Mexican cartels with the U.S. military.

“The cartels have Mexico in a python-like stranglehold,” Barr wrote March 2. “American leadership is needed to help Mexico break free. We can’t accept a failed narco-state on our border, providing sanctuary to narco-terrorist groups preying on the American people.”

On Monday, Sen. Lindsey Graham, R-S.C., said he would introduce legislation designating Mexican cartels foreign terrorist organizations and granting Biden authorities to use American troops in Mexico. Graham made the announcement after four Americans were kidnapped in the Mexican border city of Matamoros. Two of those individuals were found dead on Tuesday.

Panetta on Wednesday told Dalton that he understood the calls for the United States to do more in Mexico, including using its military, without explicitly endorsing the idea.

Dalton said she was preparing to fly to Mexico after the hearing to meet with officials there to discuss myriad security topics including intelligence and cyber cooperation. She did not rule out discussing U.S. troop presence in Mexico.

In Air Force Gen. Glen VanHerck’s prepared testimony for the hearing, the commander of U.S. Northern Command labeled drug cartels in Mexico one of his top concerns. The cartels are well-armed and have been emboldened recently by using improvised explosive devices and small drones to attack Mexican security forces, he wrote.

While VanHerck committed to continuing to partner with the Mexican military to counter cartels, he told House lawmakers that decisions about the deployment of American forces into that country were not his to make.

“If directed to plan and execute and use military force then I would do that,” VanHerck said.

But the general also told lawmakers that the drug problem, which kills some 100,000 Americans each year, was largely a homeland security and law enforcement issue not easily solved by the U.S. military, which is barred by federal law from conducting law enforcement operations inside the homeland. He told the panel increased information and intelligence sharing between U.S. institutions and Mexico and other regional partners would be a starting point to better address the cartels and drug smuggling.

“I think everybody can do more than we are right now to look at this problem, [the Mexicans] are doing a significant amount, they have tens of thousands of forces applied to the problem [but] the problem just continues to grow,” he said.

VanHerck and Dalton testified Wednesday alongside Army Gen. Laura Richardson, who leads the U.S. Southern Command. She linked China to cartel and drug activity in her area of responsibility, which encompasses South America, most of Central America and the Caribbean.

Richardson warned the Chinese were making inroads to garner more influence in South America, often using their predatory infrastructure program — known as the belt and road initiative — to exploit struggling countries. While China has not built a military base in South America, as it has in Africa, she warned Beijing could aim to do so within seven to 10 years.

Richardson also warned the Chinese were exploiting and contributing to cartel violence in the region.

Cartels use Chinese banking institutions to launder money, Richardson alleged. She said seven Chinese banks have opened some 275 branches in the SOUTHCOM region, which transnational criminal organizations have used to launder millions of dollars obtained through drug and human trafficking and illegal mining and logging.

She and VanHerck also charged many of the chemicals that the cartels use to make fentanyl flow from Chinese vendors. While China banned fentanyl production in 2019 under international pressure, the U.S. generals testified Wednesday that Beijing does nothing to stop the drugs or ingredients produced in China from flowing into the United States. VanHerck said the U.S. has unsuccessfully raised the issue with the Chinese government.

“It comes from individuals and companies in China, but the [People’s Republic of China] themselves are turning a blind eye,” VanHerck said. “So it's crucial that we expose it — that we name and shame their activities.”