My research sheds light on what triggers these incidents. Using the UCR data from 2001 to 2014, I examined the total number of incidents in each state in each week. I categorized incidents as involving either violence and intimidation or vandalism. Four factors stand out as important — two that drive violence and two that drive vandalism

Anti-Semitic vandalism

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Jewish candidates for Senate. In the past two decades, at least 10 percent of U.S. senators have been Jewish — even though Jews make up less than 2 percent of the U.S. population. This overrepresentation is frequently used as evidence for anti-Semitic conspiracies. During the climax of a campaign, states with Jewish senatorial candidates see an increasing number of incidents of anti-Semitic vandalism. (The same may apply to Jewish candidates for the House of Representatives, but I don’t have comparable data for House districts.) Major Jewish holidays. The four most prominent Jewish holidays celebrated in the United States are Rosh Hashanah, Yom Kippur, Hanukkah and Passover. That’s when anti-Semitic vandalism goes up as well, regardless of the size of a state’s Jewish population. For instance, this year, just before Yom Kippur, vandals sprayed swastikas and other Nazi symbols at the Temple Beth Shalom cemetery in Warwick, N.Y.

Anti-Semitic violence and intimidation

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Hate groups. According to the Southern Poverty Law Center , 892 hate groups are active across the United States. Of these, 521 groups are significantly hostile toward Jews, including white nationalists, racist skinheads, neo-Nazis, Holocaust denial groups and the Ku Klux Klan.The two states with the most anti-Semitic hate groups are Texas, with 62, and California, with 31. When more hate groups operate in a state, this unsurprisingly increases the likelihood of anti-Semitic violence and intimidation. An example of such targeting by hate groups occurred in San Diego , where three Jewish institutions opened handwritten letters from the “W.A.R.-White Aryan Resistance” containing anti-Semitic epithets and threatening the murder of Jews. Major Israeli military operations. Since 2001, Israel has conducted six military operations that resulted in at least 100 opposition casualties. Each of these operations triggered increases in anti-Semitic violence and intimidation in the United States. For example, during Israel’s airstrikes in the Gaza Strip in 2014, Maryland restaurant owner Benny Fischer flew an Israeli flag alongside a U.S. American flag outside Benny’s Bar and Grill — and said that during the night he received a call threatening his life

What did not lead to more anti-Semitic incidents?

Because of common anti-Semitic conspiracy theories that Jews secretly control the government or the news media and are trying to influence voters, I wondered whether anti-Semitic incidents would go up during presidential elections. They don’t. Of course, we don’t yet have 2016 data, and it is possible that anti-Semitic incidents increased in this election year. Donald Trump’s rhetoric — which has, at times, echoed and amplified that of hate groups — could have had an effect similar to having many hate groups in a state or region. But we don’t yet know this.

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These findings also suggest ways that anti-Semitic violence and vandalism could be prevented. During Jewish holidays or during an election with a Jewish candidate for senator, more careful monitoring of Jewish landmarks could help prevent anti-Semitic vandalism. When Israel is engaged in a major military operation, law enforcement agencies could increase patrols of Jewish communities, and Jewish individuals might wish to take steps to counteract their increased risk of violence and intimidation. And states with more hate groups may consider devoting extra resources to combating their influence.