The survey was published Wednesday, as Jewish communities were preparing to mark the first anniversary of the Oct. 27, 2018, mass shooting at Pittsburgh’s Tree of Life synagogue. With 11 killed, it was the deadliest known attack on Jews in U.S. history.

“American Jews could not be clearer about the reality of antisemitism in the U.S.,” David Harris, CEO of the AJC, said in a statement . “This hatred is real, comes from multiple sources, and is growing. It needs to be taken seriously and dealt with in a sustained, multi-pronged response.”

About 88% of American Jews believe anti-Semitism is a problem in the U.S. today, with 38% labeling it a “very serious” problem, according to a national survey of Jewish adults commissioned by the American Jewish Committee. A plurality of respondents (43%) said they believe anti-Semitism in the U.S. has “increased a lot” over the past five years.

Esther Wayne / SOPA Images via Getty Images Children pay their respects at a memorial site outside the Tree of Life synagogue in Pittsburgh on Oct. 31, 2018.

Nearly one year after the massacre, greater fears about anti-Semitism appear to have had significant effects on Jewish communities. Not only are Jewish institutions boosting security measures, but the AJC report also suggests that some American Jews are changing their behaviors and the way they present their religious identities in public.

Nearly one-third of respondents said they have avoided publicly wearing, carrying or displaying items ― like a Star of David pendant or a kippah ― that might help people identify them as Jewish. Young adults between 18 and 29 were the age group most likely to say they’ve hidden their Jewishness in public, with 38% saying they’d done so.

A quarter of respondents said they have avoided certain places, events or situations out of concern for their safety or comfort as Jews.

While most said they haven’t personally experienced a physical anti-Semitic attack, some said they have been the target of an anti-Semitic remark ― including 21% online and 23% in person, by mail or by phone. Most chose not to report the incidents to Jewish organizations or the police.

Forty-seven percent said that a Jewish institution they’re affiliated with has been targeted with anti-Semitic graffiti, attacks or threats. Even more said that a Jewish institution they’re affiliated with has hired security guards (57%) or has police posted at their location (52%).

When asked about the sources of anti-Semitism, respondents were more likely to say these threats come from the “extreme political right” (89%) than from the “extreme political left” (64%). About 85% said that extremism in the name of Islam also contributes to anti-Semitism in the U.S. today.

American Jews, who overall tend to lean Democratic, made it clear in the AJC survey that they are not fans of President Donald Trump. About 76% said they have an unfavorable view of the job Trump is doing and 73% said they disapprove of the way Trump is handling the threat of anti-Semitism in this country. The respondents were also more likely to say that the Republican Party, rather than the Democratic Party, bears responsibility for the current level of anti-Semitism.

The AJC’s Washington director, Alan Ronkin, said in a statement that he believes the rhetoric used during the 2016 election season, as well as the 2017 Unite the Right rally in Charlottesville, Virginia, awakened many Jews to the uptick in anti-Semitism.

“Everything changed in 2016, at least in this town,” Ronkin said. “Charlottesville got a lot of people’s attention. It really put people on notice, and they began to see things in their own towns.”