In a new era of campus upheaval, the 1970 Kent State shootings show the danger of deploying troops to crush legal protests

Ohio National Guard soldiers move in on war protesters at Kent State University on May 4, 1970. AP Photo by Brian VanDeMark, United States Naval Academy Republican presidential candidate Donald Trump has expressed his intention, if elected to a second term, to use the U.S. armed forces to suppress domestic protests. The New York Times reports that Trump’s allies are marshaling legal arguments to justify using National Guard or active-duty military troops for crowd control. Moreover, as the Times notes, Trump has asserted that if he returns to the White House, he will dispatch such forces without waiting for state or local officials to request such assistance. I am a historian who has written several books about the Vietnam War, one of the most divisive episodes in our nation’s past. My new book, “Kent State: An American Tragedy,” examines a historic clash on May 4, 1970, between anti-war protesters and National Guard troops at Kent State University in Ohio. The confrontation escalated into violence: Troops opened fire on the demonstrators, killing four students and wounding nine others, including one who was paralyzed for life. In my view, the prospect of dispatching troops in the way that Trump proposes chillingly echoes...