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

By the busload and planeload, National Guard troops were pouring into the nation’s capital on Saturday, as governors answered the urgent pleas of U.S. defense officials for more troops to help safeguard Washington even as they keep anxious eyes on possible violent protests in their own states.