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There has been no entrance to the Capitol for visitors except through the Capitol Hill Visitors Center for probably a decade. It was built after two Capitol Hill police officers were shot in 1998, after September 11, 2001, and after the Anthrax scare at the Hart Senate office building shortly after 9/11. Security at the entrance is like an airport - with metal detectors and a luggage search.
There is no way Officers were authorized to just open doors and let people in. Period.
https://www.visitthecapitol.gov/frequently-asked-questions
What special security features were built into the Capitol Visitor Center?
Improving the security of the Congress, the Capitol, and visitors was one of the fundamental goals driving the construction of the Capitol Visitor Center.
The fatal shootings of two U.S. Capitol Police officers in July 1998 and the events of September 11 underscored the degree to which the Capitol and its occupants are at risk. Therefore, Congress directed the Architect of the Capitol to design and construct a visitor center to “provide greater security for all persons working in or visiting the United States Capitol and to provide a more convenient place in which to learn of the work of Congress.”
The Visitor Center provides a secure public environment to welcome and manage millions of visitors and to protect the Capitol Building, its occupants, and guests.