The Council on American-Islamic Relations, located a few blocks south of the Capitol, was evacuated for a few hours Thursday afternoon. CAIR spokesman Ibrahim Hooper told Roll Call that a white powdery substance was received in a letter and several staffers were quarantined inside the building.

Hooper told reporters just before 3 p.m. that initial field tests showed the substance, which was in an envelope with a hate massage, tested negative for anything dangerous. The FBI is taking over the investigation and will verify those results, which could take up to five days. It is also investigating the letter that contained the substance, which included a “hate message,” according to the CAIR spokesman, who couldn’t comment on the substance of the message.

As police examined the scene, a group of staffers were standing outside the brick building behind the police tape at the corner of New Jersey Avenue and E Street SE. The building is across the street from the Capitol Power Plant, which supplies power to the Capitol complex, and around the corner from the Democratic National Committee headquarters.

CAIR Executive Director Nihad Awad told reporters the envelope was received around 1 p.m. “We’ve been receiving quite a few threats lately,” he said.

Hooper said that the number of threats has “gone up tremendously” since the terrorist attacks in Paris on Nov. 13, the attacks in San Bernardino, Calif., on Dec. 2, and since Republican presidential hopeful Donald Trump proposed on Monday a “total and complete shutdown of Muslims entering the United States.”

“We believe that this has to do a lot with the hot and escalated political speech against American Muslims and Islam in our country,” Awad told reporters.

According to Awad, the group has been in the building for 15 years and hasn’t experienced anything like this incident. For him, the hateful rhetoric directed at Muslims is worse today than it was after the terrorist attacks of Sept. 11, 2001.

“Politicians can cause havoc and cause hysteria, can cause hate crimes, and hateful acts and speeches, to dominate the discourse,” Awad, who recently attended Friday prayers with members of Congress at a local mosque, told Roll Call. “So they have a lot of responsibilities and they have to watch their tongues.”

“I remember after 2001 attacks, there was a more coherent, more decisive political discourse to prevent acts of discrimination and backlash against American Muslims,” Awad added. “Today we feel like Islamaphobia is becoming mainstream. It’s been promoted by elite politicians, by people who are trying to seek office on the backs of innocent people.”  

Asked if he was referring to Trump, Awad said, “Donald Trump is on the top of the list, but also other people.”  

The two Muslim members of Congress echoed Awad in a call with reporters Tuesday afternoon, which took place as the investigation at CAIR was unfolding.

“I am sorry that they had to suffer this tremendous assault,” Rep. Keith Ellison, D-Minn., told reporters on a phone call denouncing Republicans’ rhetoric against Muslims.

Ellison, one of only two Muslims in Congress, said when good-faith members of the community don’t speak out against hateful rhetoric — like that used by GOP presidential candidate Donald Trump recently — they “sort of green light the wicked to do what they do.”

If Muslims stand up against those who say hateful things, then maybe those who are thinking about sending a suspicious package or doing other things to attack the community would stay in the woodwork, Ellison added. “It’s critical that we denounce this rhetoric by others,” he said.

Rep. André Carson, D-Ind., is other Muslim member of Congress and was also on the call with reporters. He said he received a death threat a few days ago that was unlike the several others he has received since he was elected to Congress in 2008.

“Given the toxicity in the environment it stood out,” he said.

Carson said the Capitol Police have identified the source of the threat, but he did not provide further information.

“It’s always concerning to get these kinds of threats, but the threats aren’t going stop me from serving,” he said.

Capitol Police spokeswoman Capt. Kimberly A. Schneider wrote in an email Thursday afternoon that Capitol Police currently have “an active, open investigation” regarding the Carson threat.

Related:

Democrats Visit Mosque to Support Muslim Community GOP Elders Critical of Trump’s Muslim Comments In Washington, a Failure to Act to Counter Homegrown Terrorism | Opinion

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