The oppression of intellectuals is usually the first step towards oppressing a lot of other people, and it's also a means for the state to cement power. He's Jewish and his work focuses on the memory of the Holocaust in Europe. It's not stupid to think that, with an anti-Semite serving as the intellectual force in the White House, we will see more Jewish Holocaust historians turned away at our airports. Still, it's more likely that Rousso was detained in spite of his credentials. He was born in Egypt. I don't think the Customs people have gotten a "Keep the rat-faced Jews and the subversive foreign intellectuals out" memo yet.
I read The Vichy Syndrome six years ago, during my second year of graduate school. I was writing a not-very-good seminar paper on how the development of Holocaust memorialization in France can be seen in various films made by New Wave directors after the central period of the New Wave had ended. The book is an examination of the guilt of intellectuals, the frustration with getting the populace to acknowledge or think about the Holocaust. In one of the more interesting passages, Rousso talks about the elite class who hated the gross, sentimental Holocaust mini-series which showed on French television in 1979, but who had to concede that the show marked the first time a large percentage of the French population was willing to talk about the subject.
In another 50 years, a historian will write a book about the Trump Syndrome. He may pass over the story of Rousso, a footnote of a footnote of a footnote of Trumpism, and he will read maybe a few different historians who will try to explain the story, explanations which will likely be affected by Trump's future actions against Muslims, Jews, intellectuals, and immigrants. We may learn the full story about Rousso's detainment. We probably won't, and that's what makes it so terrifying.