November 9, 1938, started as just another day for Jews in Germany, Austria and the Sudetenland. After breakfast, fathers went to work, children went to school and mothers kissed their loved ones goodbye. They returned home for a family dinner, went to bed and expected the next day to be identical.

That night, Nazi storm troopers, aided by citizen rioters, burned 267 synagogues, vandalized 7,500 Jewish businesses, murdered 91 Jews and incarcerated 30,000 Jewish men, transferring them to newly built concentrations camps. Overnight, the Holocaust had officially begun.

Kristallnacht — the night of broken glass — marked an important turning point in Hitler’s anti-Semitic policy. Historians uniformly point out that the passivity with which German citizens accepted this violence signaled to the Nazi regime that the public was prepared for their more radical measures aimed at removing Jews entirely from German economic and social life. The Nazis were organized, they were well funded and they were united behind a single mission.

After this summer’s Operation Protective Edge, the trend of declining global anti-Semitism sharply reversed. Daily reports of vandalism, violence and intimidation of Jews all over the world has become the new normal. Classicanti-Jewish tropes have resurfaced, masquerading as critiques of Israel’s political policies and support for Palestinian human rights.

Closer to home, Students for Justice in Palestine, a well-organized group that advocates aggressive and intimidating anti-Israel tactics, is spreading its presence on college campuses throughout the U.S. at an alarming rate. Since June 2014, SJP has formed 28 new chapters, according to the Israel on Campus Coalition (ICC), bringing the nationwide total to 157.

SJP is sponsored by American Muslims for Palestine, a group that promotes and defends posting mock eviction notices on Jewish students’ dorm rooms as “constitutionally guaranteed political speech.”

Kristallnacht was a unique and extreme event that caught its victims completely off guard. Despite mounting evidence, we must remain calm and optimistic, but we must also be alert and vigilant. We must challenge those who claim their blatantly anti-Semitic rhetoric and actions are simply robust exchanges of ideas. Most importantly, we must not be afraid to act. For, in the words of Ayaan Hirsi Ali, “tolerance of intolerance is cowardice.” It is also dangerous.

This originally appeared in the Jewish Journal on November 6, 2014.