The killings also rekindled the national debate about how to assure safety at places of peace like synagogues, mosques and churches. In the wake of church massacres in Charleston, S.C., and in Sutherland Springs, Tex., some churches in states that allow people to carry concealed weapons encouraged members to bring their guns. President Trump said on Saturday that “if there was an armed guard inside the temple, they would have been able to stop” the shooter.

But Pittsburgh’s Democratic mayor, Bill Peduto, said on “Meet the Press” on Sunday that more guns were not the solution. “I don’t think that the answer to this problem is solved by having our synagogues, mosques and churches filled with armed guards.”

On Sunday afternoon, the mayor of New York City, Bill de Blasio, told an interfaith gathering at another synagogue: “Houses of worship do not have to have armed guards to be able to practice their religions.

“That’s not America,” added Mr. de Blasio, also a Democrat, at Temple Emanu-El on the Upper East Side, one of the city’s most prominent Reform synagogues.

A city councilman from the Upper West Side who is Jewish, Mark Levine, said, “I think that there is no freedom of religion in a society that requires you to carry a gun while you pray.” He added, “I don’t want to have to sit next to someone carrying a gun in the pews.”

And Rabbi Jonah Dov Pesner, director of the Religious Action Center of Reform Judaism, said in a statement, “Our synagogues cannot become bunkers.”

But some Jewish leaders in New York said that they would feel more secure knowing that an attacker entering a synagogue would face someone with the power to stop them.