The list of horrific antisemitic attacks in the United States keeps growing. Two weeks ago in Boulder, Colo., a man set fire to peaceful marchers who were calling for the release of Israeli hostages. Less than two weeks earlier, a young couple was shot to death while leaving an event at the Jewish Museum in Washington. The previous month, an intruder scaled a fence outside the official residence of Gov. Josh Shapiro of Pennsylvania and threw Molotov cocktails while Mr. Shapiro, his wife and children were asleep inside. In October, a 39-year-old Chicago resident was shot from behind while walking to synagogue.

The United States is experiencing its worst surge of anti-Jewish hate in many decades. Antisemitic hate crimes more than doubled between 2021 and 2023, according to the F.B.I., and appear to have risen further in 2024. On a per capita basis, Jews face far greater risks of being victims of hate crimes than members of any other demographic groups.

American Jews, who make up about 2 percent of the country’s population, are well aware of the threat. Some feel compelled to hide signs of their faith. Synagogues have hired more armed guards who greet worshipers, and Jewish schools have hired guards to protect children and teachers. A small industry of digital specialists combs social media looking for signs of potential attacks, and these specialists have helped law enforcement prevent several.

The response from much of the rest of American society has been insufficient. The upswing in antisemitism deserves outright condemnation. It has already killed people and maimed others, including an 88-year-old Holocaust survivor who was burned in Boulder. And history offers a grim lesson: An increase in antisemitism often accompanies a rise in other hateful violence and human rights violations. Societies that make excuses for attacks against one minority group rarely stop there.

Antisemitism is sometimes described as “the oldest hate.” It dates at least to ancient Greece and Egypt, where Jews were mocked for their differences and scapegoated for societal problems. A common trope is that Jews secretly control society and are to blame for its ills. The prejudice has continued through the Inquisition, Russian pogroms and the worst mass murder in history, the Holocaust, which led to the coining of a new term: genocide.