The Trump administration is revoking visas for Chinese students “with connections to the Chinese Communist Party or studying in critical fields” and revising its “visa criteria to enhance scrutiny of all future visa applications” for students from China and Hong Kong.

This is both necessary and long overdue. For years, China has been engaged in a systematic effort to target U.S. universities, using Chinese students to conduct extensive espionage and intellectual property theft on elite campuses across the United States — which has helped fuel China’s technological and military growth.

To understand how China uses its students as spies, read the stunning investigative report published last month by Stanford Review reporters Garret Molloy and Elsa Johnson in which they documented the infiltration of Stanford University by the Chinese Communist Party. “The CCP is orchestrating a widespread academic espionage campaign at Stanford,” Johnson told me and my co-host, Danielle Pletka, in a recent podcast interview. “Stanford is in the heart of Silicon Valley,” she added, “and that’s a huge incentive for China.”

Johnson and Molloy interviewed Chinese nationals on campus who told them how the espionage works. “In conversations, Chinese students would report, ‘Every single week I’m asked to meet a handler where I’ll be asked to talk about the research I’m doing, the directions that research is going in, how that research is progressing and how we could reimplement that research back in China,’” Molloy said. If their handlers “have interest in, let’s say, [artificial intelligence] or quantum computing,” he said, “they will then reach out to that student and ask them to provide documents, internal memos, methodologies, future directions of the research.”

Some conduct espionage for Beijing willingly. “There are some students who want to work with the Chinese government and they’re happy to do this, they want to advance their careers,” Johnson said. Others are victims of what the reporters call “transnational repression,” in which the long arm of Chinese state security reaches across the Pacific into the United States. In 2017, China passed a National Intelligence Law mandating that Chinese citizens must “support, assist, and cooperate with state intelligence work,” whether at home or abroad.

“At Stanford, students who refused to hand over certain documents had their family taken to police stations in China,” Molloy told me, adding, “if you do not comply with the national intelligence law, your family back in China is under threat. Therefore, students have a very strong incentive to do exactly what the party says.” What this means is, whether enthusiastically or reluctantly, countless Chinese nationals at U.S. universities must inform on their schools to the Chinese Communist Party.

Stanford is not alone. There are approximately 277,398 Chinese students in the United States, according to the Institute of International Education, second only to India in terms of U.S. enrollment. The majority are studying science, technology, engineering and mathematics — areas of high priority for CCP espionage.

Nearly half of Chinese students are pursuing advanced degrees. Many graduate students are sponsored by state-backed vehicles, such as the China Scholarship Council, which the Chinese regime uses to recruit and pay tuition for Chinese students chosen to attend, and almost certainly spy on, U.S. universities. CSC-funded students are must pass party loyalty tests, Molloy said, and are “required to go to the Chinese consulate and provide information” on research taking place at the university as well as conduct “peer surveillance” of other Chinese nationals.

Stanford and other universities appear more than happy to look the other way and take Beijing’s money, which has become a major source of revenue for U.S. universities. Indeed, an investigation by the Free Press found that China has become the second-largest source of foreign funding for U.S. universities, behind only Qatar.

Rep. John Moolenaar (R-Michigan), chairman of the House select committee on China, recently wrote to the presidents of Stanford, Carnegie Mellon, Purdue, the University of Illinois, the University of Maryland and the University of Southern California warning that “America’s student visa system has become a Trojan horse for Beijing, providing unrestricted access to our top research institutions and posing a direct threat to our national security.”

He asked them to provide Congress with detailed information on Chinese national undergraduate, graduate and PhD students attending their institutions, including: the sources of tuition funding for Chinese nationals at their schools; the type of research Chinese national students are conducting; and what policies are in place to prevent Chinese nationals from working on projects tied to U.S. government grants and export-controlled coursework, such as advanced semiconductor engineering, quantum computing, AI and aerospace engineering.

Molloy, an economics major, visited China last summer and was shocked to meet with many members of the CCP who were educated at Stanford. “We’re educating the head of the Chinese [securities and exchange commission], we’re educating the head of Beijing’s tariff negotiators. I’m meeting all these people and they all say ‘I work for the Chinese Communist Party in a really high role. I hope that China beats the U.S. And I also went to Stanford for my undergraduate and master’s degree.’ And I’m putting this together and I’m saying it’s shocking that we are educating such high-level Communist Party officials. … What’s going wrong here?”

It’s a fair question — one of many for which the Trump administration plans to get answers.

Marc Thiessen writes a column for The Washington Post on foreign and domestic policy.