A protester shouting “Trump is treason” threw Russian flags from within the press stakeout at the Capitol on Tuesday as President Donald Trump walked with Senate Majority Leader Mitch McConnell.

United States Capitol Police later identified the protester as Ryan T. Clayton, 36, of Sterling, Virginia. A Capitol Police spokeswoman said Sterling was arrested and preliminarily charged with unlawful conduct. 

Clayton did not hold any kind of press credential, according to Senate staffers.

Trump did not respond to questions from reporters as he made his way to the Senate Republicans’ weekly policy lunch.

Just before that incident, at least three senators were asked to present identification to Capitol Police.

Clayton managed to hide among a press group waiting for the president but Republican Sens. Roy Blunt of Missouri, Rob Portman of Ohio and John Hoeven of North Dakota were stopped by Capitol Police officers while trying to walk across the East Front of the Capitol. All three have served in the Senate since 2011.

Capitol Police officers are trained to ask for identification if they do not recognize a senator.

Secret Service joined Capitol Police on the Hill to control movement in the area where the president would walk on the first floor and to secure the press scrum on the second floor.

To get in, Clayton would have needed to be escorted by somebody with proper identification or he could have snuck past security possibly via the Capitol Visitor Center. He was not wearing a badge. Escorted visitors receive a sticker when they enter, which he was also not wearing at the time of the protest.

The Capitol Police spokeswoman did not respond to Roll Call’s specific questions on Clayton, and about the senators not being recognized. 

Capitol Police have in the past been criticized by members for not recognizing them. South Carolina GOP Sen. Tim Scott last year described being forced to show his identification on multiple occasions.

In 2006, Rep. Cynthia A. McKinney got into a physical altercation with a Capitol Police officer who tried to stop her from going around a metal detector, which members are allowed to do. The Georgia Democrat was not wearing her member pin at the time. McKinney said she was defending herself against an officer who racially profiled her and touched her inappropriately, according to reports at the time.

Watch: The Moment Trump Arrives at Hill Lunch, a Protester Interjects

Alex Gangitano, Niels Lesniewski, Joe Williams and Griffin Connolly contributed to this report.