After a massacre at a Pittsburgh synagogue Saturday, President Donald Trump suggested armed guards belong at houses of worship — a safety measure the Jewish community has deployed for at least two decades, security experts said.

“If they had protection inside, the results would have been far better,” Trump said after the shooting that left 11 dead and six injured, two critically.

Many security experts consider houses of worship “soft targets” — places that are especially vulnerable to potential attacks, and Jewish institutions often view beefed-up security as a necessity in a world that presents constant threats.

Deadly shootings across denominations in recent years include 26 killed at a church in Sutherland Springs, Texas, in 2017; nine at a church in Charleston, South Carolina, in 2015; six at a Sikh temple in Oak Creek, Wisconsin, in 2012; and three at a Jewish Community Center in Overland Park, Kansas, in 2014.

Last year, a firearms training school in Corona, California, added a "synagogue security" class to its list of courses. Previous private training sessions for synagogues were popular enough to offer a full course, said William Murphy, co-owner of Firearms Training Associates.

A Los Angeles Police Department patrol car is parked outside the Simon Wiesenthal Center as center staffers walk in front of the building in Los Angeles on June 11, 2009, a day after a white supremacist shot and killed a guard at the U.S. Holocaust Memorial and Museum in Washington, D.C. Reed Saxon / AP file

The synagogue security class includes how to use a handgun to stop an attacker, he said.

"We believe in an armed response," Murphy said. "There's no way to stop a crazy guy with a gun if there isn’t a gun on site."

Chuck Diamond, a former rabbi at the synagogue who retired more than a year ago, said off-duty police are hired to work security during the high holidays in the fall, but otherwise there are no guards, and the entrance is open during sabbath.

"It's a nice community," he said.

Jewish institutions have long been targets for domestic terrorists and often deploy armed security, said Rabbi Abraham Cooper, social action director at the Simon Wiesenthal Center in Los Angeles.

It’s a policy that gained new urgency after the 1999 shooting at the North Valley Jewish Community Center in Los Angeles that wounded five, including three young children. Many Jewish institutions beefed up security, and the Los Angeles Police Department increased patrols of houses of worship.

"The wake-up call back then definitely had an impact on Jewish institutions," Cooper said.

But, he added, there probably will always be softer targets.

In 1999, white supremacist Buford O. Furrow Jr. drove from Tacoma, Washington, to Los Angeles in search of victims but bypassed the Simon Wiesenthal Center because tight security there “sent him looking for an easier target,” according to an account posted online by the center.

Cooper said high-profile security at two other Jewish institutions in Los Angeles prevented Furrow, now serving life at a federal penitentiary, from attacking them.

That’s the point of good security, but it also means a determined attacker will eventually find victims, Cooper said.

"You have serious security on your perimeter, chances are, as with Buford Furrow, the individual might look somewhere else," he said.

Safdar Khwaja, president of the Pittsburgh chapter of the Council on American Islamic Relations, said his organization advised all area mosques to increase security after the synagogue shooting.

In the past few years, Khwaja said, “a lot” of mosques have reached out to ask for guidance on how to keep their attendees safe, with many asking if they should have an armed guard.

“It’s a very sad state of affairs,” Khwaja said. “Some feel that they’re secure, but they may not be.”