Only hours after news broke that a suspect in a mass shooting in San Bernardino, Calif., had a Muslim name, the well-practiced organizations that represent American Muslims to the broader public kicked into action, as they routinely do after each terrorist attack attributed to Muslim extremists.

They issued news releases condemning the attacks as inhuman and un-Islamic, posted expressions of grief on Facebook and held news conferences in which Muslim leaders stood flanked by American flags alongside clergy of other faiths and law enforcement officials.

“Groups like ISIS and Al Qaeda,” Salam al-Marayati, president of the Muslim Public Affairs Council, said at a news conference in Los Angeles on Thursday, “are trying to divide our society and to terrorize us. Our message to them is we will not be terrorized and we will not be intimidated,” either by the terrorists or, he said, “by hatemongers who exploit the fear and hysteria that results from incidents like this.”

But the message is apparently not getting through. Muslims and leaders of mosques across the United States say they are experiencing a wave of death threats, assaults and vandalism unlike anything they have experienced since the aftermath of the Sept. 11 terrorist attacks in 2001.