Troops Flood a Rattled Washington Ahead of the Biden Inauguration

“We do not tolerate extremists in our ranks,” Pentagon spokesman Jonathan Hoffman told reporters.

Beyond the Capitol building, the Secret Service is establishing a “healthy, layered buffer” with vehicle checkpoints, metal detectors and additional security screenings to prevent another deadly siege, Mr. Plati said.

“Obviously the Capitol is a significant event,” he said. “We are sensitive to that. We constantly are evaluating our security plans. There’s always lessons that can be learned after an event of that nature.”

To avoid the breakdowns in coordination among law enforcement agencies that left badly outnumbered Capitol Police overwhelmed last week, Mr. Plati said the Secret Service would be working out of a “multiagency coordination center” with other law enforcement leaders to make quick decisions about the movements of any protesters and make additional deployments.

“We’re going to create a bubble that is safe and secure,” Mr. Plati said.

With far-right extremists continuing to plot on online platforms, one senior Pentagon official called the security situation “unprecedented.”

Another Defense Department official said that law enforcement agencies were planning for any number of possible events, some of them horrific. Worst-case scenarios include snipers targeting inauguration dignitaries, “suicide-type aircraft” entering Washington’s restricted airspace, and even remote-powered drones attacking the crowd. The officials said they were particularly worried about multiple active-shooter situations flaring up simultaneously.

Defense Department officials have not made a final decision on whether National Guard troops will be armed; but even if they are initially unarmed, the troops will not be far away from their weaponry, the officials said. Troops will be equipped with at least defensive riot gear, like helmets.

“We want our individuals to have the right to self-defense,” General Hokanson said during a news briefing. “If senior leadership determines that that’s the right posture to be in, then that is something we will do.” All of the troops coming to Washington, he said, are bringing their guns with them.