The accused Hamas sympathizer is shrouded in mystery—and so are his supporters. As it unfurls, the saga of Mahmoud Khalil—the Columbia agitator picked up by immigration enforcement last week—looks less like a complicated immigration-law dispute and more like something out of a John le Carré novel. But inspect the details, and Khalil’s case gives us a glimpse a well-established network linking American universities, international progressive NGOs, and government agencies. This network places ideologues like Khalil in positions of power and influence and promoting radical policies that challenge both the will of American voters and our national-security interests. As always in...