Snyder, a son of Quakers and an Oxford-educated Yale professor, is a specialist in Central and Eastern European history and the Holocaust. He is the author of “Bloodlands,” “On Tyranny,” and other well-received books. In this compelling video, Snyder describes the threat posed by Trump and his followers, and makes clear it hasn’t gone away. To those well-read in history, Snyder’s phraseology — “faith in a leader,” “the big lie,” and “stab in the back” — evokes association with another historical context.