Washington is locked down and U.S. law enforcement officials are geared up for pro-Trump marches in all 50 state capitals this weekend, erecting barriers and deploying thousands of National Guard troops to try to prevent the kind of violent attack that rattled the nation January 6.

The FBI warned police agencies of possible armed protests outside all 50 state capitol buildings starting Saturday through President-elect Joe Biden's inauguration on January 20, fueled by supporters of President Donald Trump who believe his false claims of electoral fraud.

A barricade is seen at the top of the steps leading to the front entrance of the Pennsylvania Capitol, Jan. 16, 2021, in Harrisburg. At capitols across the country, National Guard troops are being called up, fences built, and barricades positioned.

Michigan, Virginia, Wisconsin, Pennsylvania and Washington were among states that activated their National Guards to strengthen security. Texas closed its Capitol through Inauguration Day. Steve McCraw, director of the Texas Department of Public Safety, said in a statement late Friday that intelligence indicated "violent extremists" might seek to exploit planned armed protests in Austin to "conduct criminal acts."

In downtown Washington, officers arrested a Virginia man who tried to pass through a Capitol Police checkpoint Friday carrying fake inaugural credentials, a loaded handgun and more than 500 rounds of ammunition, CNN and The New York Times reported Saturday, citing a police report and a law enforcement source. The man was charged with five crimes, including illegal possession of a weapon and ammunition, according to the report.

Capitol Police officials could not be reached for comment.

States respond

The scramble followed the deadly January 6 attack on the U.S. Capitol in Washington by a mix of extremists and Trump supporters, some of whom apparently planned to kidnap members of Congress and called for the death of Vice President Mike Pence as he presided over the certification of Biden's victory in November's election.

A law enforcement official sweeps a spectator seating area as preparations take place for President-elect Joe Biden's inauguration ceremony at the U.S. Capitol in Washington, Jan. 16, 2021.

The Democratic leaders of four U.S. congressional committees said Saturday that they had opened a review of the events and had written to the FBI and other intelligence and security agencies to find out what was known about threats, whether the information was shared and whether foreign influence played any role.

"This still-emerging story is one of astounding bravery by some U.S. Capitol Police and other officers; of staggering treachery by violent criminals; and of apparent and high-level failures - in particular, with respect to intelligence and security preparedness," said the letter.

It was signed by House Intelligence Chairman Adam Schiff, House Homeland Security Chairman Bennie Thompson, House Oversight Chairwoman Carolyn Maloney and House Judiciary Chairman Jerrold Nadler.

Law enforcement officials have trained much of their focus on Sunday, when the anti-government "boogaloo" movement plans to hold rallies in all 50 states.

In Michigan, a fence was erected around the Capitol in Lansing and troopers were mobilized from across the state to bolster security. The legislature canceled meetings next week, citing concern about credible threats.

A Mississippi State Capitol police officer watches the main entrance on the north side of the statehouse in Jackson, Jan. 15, 2021. State capitols across the country are under heightened security ahead of Joe Biden's inauguration as president.

"We are prepared for the worst, but we remain hopeful that those who choose to demonstrate at our Capitol do so peacefully," Michigan State Police Director Joe Gasper told a news conference on Friday.

Extremist groups

The perception that the January 6 insurrection was a success could embolden domestic extremists motivated by anti-government, racial and partisan grievances, spurring them to further violence, according to a government intelligence bulletin dated Wednesday that was first reported by Yahoo News.

The Joint Intelligence Bulletin, produced by the FBI, Department of Homeland Security and National Counterterrorism Center, further warned that "false narratives" about electoral fraud would serve as an ongoing catalyst for extremist groups.

Thousands of armed National Guard troops were in the streets in Washington in an unprecedented show of force after the assault on the U.S. Capitol. Bridges into the city were to be closed, along with dozens of roadways. The National Mall and other iconic U.S. landmarks were blocked off into next week.

Christian Alvarado holds a U.S. flag in front of a fence surrounding the California Capitol in Sacramento, Jan. 16, 2021. The fence was built because of concerns that protests around Joe Biden's inauguration as president Jan. 20 could turn violent.

Experts say that the capitals of battleground states such as Wisconsin, Michigan, Pennsylvania and Arizona are among those at most risk of violence. But even states not seen as likely flashpoints are taking precautions.

Illinois Governor J.B. Pritzker said Friday that while his state had not received any specific threats, he was beefing up security around the Capitol in Springfield, including adding about 250 state National Guard troops.

The alarm extended beyond legislatures. The United Church of Christ, a Protestant denomination of more than 4,900 churches, warned its 800,000 members there were reports that "liberal" churches could be attacked in the coming week.

Effective deterrents

Suzanne Spaulding, a former undersecretary at the Department of Homeland Security, said authorities disclosing enhanced security measures can be an effective deterrent.

"One of the ways you can potentially de-escalate a problem is with a strong security posture," said Spaulding, now a senior adviser at the Center for Strategic and International Studies. "You try to deter people from trying anything."

Following the January 6 violence in Washington, some militia members said they would not attend a long-planned pro-gun demonstration in Virginia, where authorities were worried about the risk of violence as multiple groups converged on the state capital, Richmond.

Others told The Washington Post they wanted the protest organized in response to new state gun rules to be peaceful. Some militias across the country have told followers to stay home this weekend, citing the increased security or the risk that the planned events were law enforcement traps.