(CNN) They're supposed to be pillars of unity and peace, where both Jews and non-Jews can enjoy classes, sports and other communal activities.

But more than 80 Jewish community centers and schools have turned into targets of hate and been subjected to bomb threats as fears of heightened anti-Semitism spread across the country.

The threats have reached such a crescendo that President Donald Trump used his speech to Congress on Tuesday night to address the issue.

"Recent threats targeting Jewish community centers and vandalism of Jewish cemeteries, as well as last week's shooting in Kansas City, remind us that while we may be a nation divided on policies, we are a country that stands united in condemning hate and evil in all of its very ugly forms," the President said.

The President was referring to the toppling of dozens of Jewish headstones in cemeteries in two cities and the shooting of two Indian men in Kansas February 22 by an assailant who reportedly shouted, "Get out of my country!" One of the men died.

Law enforcement officials believe many of the threatening calls to Jewish community centers have originated overseas. So far, none of the threats have been carried out. But the lack of destruction has not made them any less chaotic or anxiety-inducing.

"This is the first time in the 60-plus years of our organization we have had a bomb threat called in. And now we've had three bomb threats this year," said the CEO of a JCC in the Northeast who wished to remain anonymous for fear of copycats targeting his center. "It's alarming."

The alarm from the bomb threats, combined with the recent vandalism at Jewish cemeteries in St. Louis and in Philadelphia, have led some to see a pattern of rising anti-Semitism.

The series of bomb threats in recent weeks has disrupted day-to-day life, sparked fear in tight-knit communities, and raised questions about what the federal government is doing to find out who's responsible. "You ask me are the feds doing enough? And I'm really not sure," the anonymous CEO said.

The waves of threats

The incidents made national news when, on January 9, 15 Jewish centers and schools received bomb threats. Since then, the threats have occurred in waves, with a series of threats on January 18, January 31, February 20.

The latest wave came Monday, with another 31 threats called in to 23 JCCs and schools -- bringing the total number of threats to 100.

Jewish community centers, or JCCs, function as hubs of communal activity for Jews and non-Jews alike. They host art and sports classes for children and adults, and help create connected communities.

The threats have not been limited to the Northeast, or to the United States. They have targeted 81 different locations, spread across 33 states and two Canadian provinces, according to data from the JCC Association of North America.

They are disrupting the routine and the feeling of security in the affected centers, with adults, children and infants forced to evacuate at a moment's notice.

But on a deeper level, the threats have functioned like terrorism, shattering the idea of safety.

Joycie Porter of Syosset, New York, and her husband were at a JCC when a bomb threat came in. She said she and a group of kids from the nursery were ushered outside until it was safe to go back in.

"It's just very disheartening," Porter told CNN affiliate News 12 Long Island. "It's really a terrible time for us."

Rick Lewis is a parent of three teenagers and the CEO of Mid-Island JCC in Plainview, New York, so the threats hit him both professionally and personally.

"It was a tiring day because not only do I have three children, but I have 250 children in my nursery school that I feel responsible for."

Parents have pulled their children from JCCs across the country since the threats began. In a JCC in Orlando, Florida, which has received two threats, 50 students have withdrawn from the school. In Albany, New York, 12 families have removed their children.

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Dr. Jaime Huysman is the parent of a student at David Posnack JCC in Davie, Florida, which received a threat on Monday. Huysman told CNN affiliate WSVN that the threat was "particularly scary."

"My father's a Holocaust survivor, and I just called him up, and he's crying on the phone," Huysman said.

In Birmingham, Alabama, the Levite Jewish Community Center has received three bomb threats in the past six weeks, including one on Monday to its N.E. Miles Jewish Day School, the center's executive director Betzy Lynch said.

Lynch said her message to worried students, parents and community members is: "We have to be resilient, be tenacious. Show up. We will continue to live life as it should be."

Lynch said 67% of the people who use the JCC are of faiths other than Jewish.

Though the threats have interrupted their day -- and caused some fear -- people are still coming to the center, she said. Only about five of the 200 families attending the center have since left. In fact, more people have joined as a sign of solidarity, she said. "People aren't standing for this," Lynch said.

Status of the investigation

The FBI said the bureau and the Justice Department's Civil Rights division are "investigating possible civil rights violations in connection with threats to Jewish Community Centers across the country."

But details on that investigation have been scarce, and it's difficult to know the extent of these threats. Are they all connected? Is this all the work of just one person, or more?

Paul Goldenberg, national director of the Secure Community Network, which advises Jewish organizations on security, said the calls are " unprecedented " for their methodical approach and their sophisticated use of voice-masking technology.

JTA News, a Jewish news service, posted audio of one of the bomb threats. In it, a disguised voice warns that a C-4 bomb has been placed in the JCC and that "a large number of Jews are going to be slaughtered."

"They could be 15 or 60 years old. These masking technologies are very effective," Goldenberg said.

"I'm in touch with the FBI frequently every day, and I know they're working on this investigation very aggressively," he said.

Jewish leaders have called for a more robust response from the government, both in word and action.

"Anti-Semitism of this nature should not and must not be allowed to endure in our communities," the JCC Association of North America said in a statement.

"The Justice Department, Homeland Security, the FBI, 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," the JCC said.

White House response questioned

The White House in particular had been a target of criticism for its response -- or the lack of one. The President did mention the threats in his speech Tuesday evening, but did not outline a plan to stop them.

Two weeks ago, Trump said a Jewish reporter had "lied" and told him to "sit down" after the reporter asked about the White House's plan to address anti-Semitism.

CNN: In response to question re threats to Jewish centers,Trump called a Jewish reporter a liar,told him to sit down https://t.co/EucdYeUzRF — Operation Pig Roast (@OpPigRoast) February 16, 2017

"No. 1, I am the least anti-Semitic person that you've ever seen in your entire life," Trump said. "No. 2, racism. The least racist person. In fact, we did very well relative to other people running as a Republican."