“The Justice Department, Homeland Security, the F.B.I. and the White House, alongside Congress and local officials, must speak out — and speak out forcefully — against this scourge of anti-Semitism impacting communities across the country,” David E. Posner, the JCC’s director of strategic performance, said in a statement. “Actions speak louder than words. Members of our community must see swift and concerted action from federal officials to identify and capture the perpetrator or perpetrators who are trying to instill anxiety and fear in our communities.”

Legislators and governors in several states condemned the threats. Sean Spicer, the White House press secretary, said at a news briefing on Monday that Mr. Trump “continues to be deeply disappointed and concerned by the reports of further vandalism” at the Jewish cemeteries.

“The president continues to condemn these and any other forms of anti-Semitic and hateful acts in the strongest terms,” Mr. Spicer said.

Barbara Perle, 66, of Los Angeles said on Monday that several of her family members were buried in the vandalized Chesed Shel Emeth Cemetery near St. Louis. That includes her great-grandfather, Nathan Blitz. Seeking religious freedom and an escape from economic oppression, he fled Russia in the early 1900s and settled in St. Louis, where he served as a rabbi and started a new life for his family.

But because all of his surviving great-grandchildren live hundreds of miles away from St. Louis, they do not know if his grave was among the 200 that were vandalized. No matter, Ms. Perle said; in her eyes, an attack on one gravestone in the Jewish cemetery was an attack on them all.

“To come to the U.S. and create this amazing life where everyone felt safe and secure and able to be who they were, that was an incredible thing coming from Eastern Europe,” Ms. Perle, a hospice medical social worker, said. “For this to have happened where my family has been laid to rest was just heartbreaking. These are unconscionable acts.”

She said that she had reached out to thank Mr. El-Messidi after reading about the effort and that she had “come to understand more about our shared humanity.”