Hundreds of New Jersey National Guard troops are among those being vetted by the FBI ahead of Joe Biden's inauguration.

Following the deadly insurrection at the Capitol on Jan. 6, Gov. Phil Murphy sent hundreds of New Jersey's citizen soldiers to Washington, D.C., to help restore the peace. He said they would remain to help provide security for Biden's inauguration as the nation's 46th president. About 25,000 guard troops from around the nation have been mobilized ahead of Wednesday's swearing-in.

U.S. defense officials say they are worried about an insider attack or other threat from service members involved in securing Biden's inauguration. That concern is prompting the FBI to vet all 25,000 National Guard troops coming into Washington for the event.

The massive undertaking reflects the extraordinary security concerns that have gripped Washington following the deadly Jan. 6 insurrection at the U.S. Capitol by pro-Trump rioters. And it underscores fears that some of the very people assigned to protect the city over the next several days could present a threat to the incoming president and other VIPs in attendance.

Dozens of current and former military personnel are being investigated for their role in the protest that devolved into insurrection, according to a spokeswoman for Army Secretary Ryan McCarthy. The L.A. Times has identified multiple individuals tied to the U.S. military who joined far-right extremists in breaching the Capitol. U.S. Army Col. Jeffrey D. McCausland, a professor of national security at Dickinson College and former dean at the U.S. Army War College, told the Times, "These are people who are supposed to uphold the Constitution and the law, yet they were doing the exact opposite.”

An Army reservist who works as a contractor at the Naval Weapons Station Earle is among those arrested in connection with the riots. Timothy Hale-Cusanelli faces five federal charges. An affidavit filed by the FBI says Hale-Cusanelli is an avowed white supremacist and Nazi sympathizer. Investigators claim an informant recorded Hale-Cusanelli talking about being part of the mob and saying they could have taken over the federal building if they had more men.

Several Democratic members of Congress have demanded the Pentagon begin an internal investigation to determine how pervasive is extremist ideology among members of the military. Senior Defense Department officials have acknowledged they have a problem with extremism, especially white supremacy, but the extent of which among the 2 million active duty personnel is unknown. The Pentagon issued a sternly worded memo to all personnel last week that reminded them of their oath, and branding violence at the Capitol "sedition and insurrection."

(The Associated Press contributed to this story.)

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