The University of Illinois board of trustees on Thursday affirmed its refusal to hire a professor who posted a series of harsh anti-Israel tweets this summer. The professor says the act is part of an effort by “wealthy and well organized groups to attack pro-Palestinian students and faculty.” The case has drawn wide attention on college campuses because it raises the issue of the suppression of academic freedom around the Israeli-Palestinian conflict—a hot-button topic at universities across the country. Steven Salaita, a Palestinian-American professor with an expertise in indigenous studies, accepted a tenure-track position last year to start working in...