Two Puerto Rican nationalists, Oscar Collazo and Griselio Torresola, attempted to assassinate President Truman on November 1, 1950. They arrived in Washington D.C. the day before from the Bronx in New York City, where they were active in the Puerto Rican Nationalist Party. They thought the assassination would call attention to Puerto Rico and advance the cause of Puerto Rican independence.
On the morning of November 1, they prepared for the assault. Torresola, a skilled gunman, taught Collazo how to load and handle a gun. They familiarized themselves with the area near Blair House, across the street from the White House, where they would stage the assault. (The Truman family stayed in the Blair House during renovation of the White House from 1948 to 1952). Collazo and Torresola planned to approach the house from opposite directions and shoot their way inside. In the ensuing gun battle, Collazo and Torresola traded gunfire with White House policemen and secret service agents. They wounded three White House policemen but never reached the interior of the house. One of the wounded policemen, Private Leslie Coffelt, managed to fire one bullet and hit Torresola in the side of the head, killing him instantly. Coffelt died later that day at the hospital. Two other policemen, Donald Birdzell and Joseph Downs, were each hit more than once but recovered from their wounds. Collazo reached the steps of Blair House before collapsing with a gunshot wound to the chest. It was later found that only one shot fired by Collazo had hit anyone�his first shot, which wounded Private Birdzell. Torresola had inflicted all the other gunshot wounds on the three White House policemen. President Truman was taking a nap upstairs in Blair House when the shooting began. He rushed to a window and saw Collazo below on the front steps. A White House guard saw the President in the window and shouted to him to him to get down. The President obeyed.
Collazo was sentenced to death for the attempt; one week before his scheduled execution in 1952, Truman commuted the sentence to life imprisonment. President Carter commuted the life sentence of Collazo in September 1979, and he was freed from prison. He died in Puerto Rico on February 20, 1994 at the age of 80.
You can learn more about the Private Coffelt here.