In the early 2000s, as the uprising known as the second intifada instilled fear in Israelis through a series of suicide bombings, Kenneth Marcus, then an official in the U.S. Department of Education, watched with unease as pro-Palestinian protests shook college campuses. Ever since, Mr. Marcus, perhaps more than anyone, has tried to douse what he sees as a dangerous rise of campus antisemitism, often embedded in pro-Palestinian activism. He has done it as a government insider in the Bush and Trump administrations, helping to clarify protections for Jewish students under the 1964 Civil Rights Act and broadening the definition of what can be considered antisemitic.