Federal, state and local law enforcement remain on high alert ahead of Saturday's "Justice for J6" protest outside of the U.S. Capitol.
Although intelligence suggests there will not be widespread or significant violence, federal law enforcement officials and groups that track domestic extremism told CBS News they remain concerned about the potential for "lone wolf"-style violence or individual "knuckleheads" using the gathering to cause trouble.
The FBI is monitoring chatter picked up on social media sites and message boards, including Telegram, Parler and Gab.
"I wouldn't say really informed people are worried" about the threat level from the online chatter, a federal law enforcement source familiar with the rally planning told CBS News. "But they are taking no chances."
Out of an abundance of caution, temporary fencing is being installed around the U.S. Capitol, the U.S. Capitol Police is requesting the National Guard Quick Reaction Force to be on standby near the Capitol, and Capitol and D.C. Metropolitan police, as well as additional officers from surrounding cities and federal agencies who have Civil Disturbance Unit training, are being activated.
Intelligence gathered to date indicates far right extremist groups including the Proud Boys and Oath Keepers are planning to attend the rally to demand "justice" for the hundreds of people that have been charged for their alleged roles in the January 6th attack on the U.S. Capitol.
The Department of Defense is reviewing the Capitol Police's request for the National Guard to be "on standby" for Saturday's rally, a department official and a congressional source familiar with the request told CBS News. The plan calls for the guard to be ready at the nearby D.C. Armory, the congressional source said.
"I don't think they will need the guard," one congressional source familiar with the intelligence said.
"The USCP has asked the Department of Defense for the ability to receive National Guard support should the need arise on September 18," a Capitol Police spokesman confirmed in a statement to CBS News.
Earlier, officials saidto attend Saturday's rally. That estimate is "holding solid," one official told CBS News.
"What I'm most worried about, and still worry about, is the threat that we do not know about. That's the threat that's going to get by," said retired FBI agent Thomas O'Connor, who spent 23 years on the Joint Terrorism Task Force in Washington, D.C. "We have to be over-prepared. We have to deal for the worst case scenario and hope for the best case scenario."
According to law enforcement sources intelligence suggests that potential incidents at Saturday's rally could be similar the isolated fights seen at demonstrations attended byin late 2020, rather than the violence displayed during the .
Groups that monitor domestic extremist behavior told CBS News many groups on their radar have not been especially vocal about this rally and some leaders of extremist groups are even encouraging their followers not to attend the rally.
The FBI and other federal agencies will have agents available to monitor developments.
In a memo sent to Capitol Hill staff Wednesday evening, the Capitol Police and the Senate Sargent at Arms wrote they "continue to monitor and prepare for the permitted demonstration activity on Saturday, September 18, 2021."
"Members and staff should expect demonstration activity and potential for street closures to impact access to the U.S. Capitol Complex," the memo said. "We are also aware and will monitor similar demonstrations being planned at some state capitols across the country."
The memo also told members the "inner perimeter fencing around Capitol Square" will be installed overnight Wednesday and work will be completed Thursday evening. The Capitol Police said they expect the fencing will come down after the rally on Sunday.
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