Last October, as protests against Israel’s war on Gaza swept U.S. campuses, two prominent pro-Israel groups wrote to nearly 200 university and college administrators urging them to investigate their students for possibly violating federal law by promoting pro-Hamas, anti-Israel messaging. The Anti-Defamation League, or ADL, and the Louis D. Brandeis Center for Human Rights Under Law suggested that members of Students for Justice in Palestine, the largest Palestine solidarity campus organization in the country, may have been violating a law that prohibits people from providing “material support” — a broad category that includes money as well as services or other...