As for 200 years:

On March 1, 1954, while Members gathered on the House Floor for an upcoming vote, three men and one woman entered the visitor’s gallery above the chamber and quietly took their seats. All four belonged to the Puerto Rican Nationalist Party and only hours earlier had traveled from New York City to Washington, DC. 

The United States had annexed Puerto Rico in 1898, and the island’s relationship with the federal government had long been a point of contention. Some Puerto Ricans sought to maintain their relationship with the mainland, and others, like the four visitors in the House that day, argued for an independent Puerto Rico.

The Capitol had few security protocols at the time, and the four Puerto Rican nationalists entered the gallery armed with handguns. Around 2:30 p.m. they indiscriminately opened fire onto the House Floor and unfurled a Puerto Rican flag in a violent act of protest meant to draw attention to their demand for Puerto Rico’s immediate independence.

Five Congressmen were wounded in the shooting.

Members, House Pages, and police officers quickly helped detain three of the assailants outside the gallery, while the fourth escaped the Capitol and was apprehended later that afternoon.