(HT: Ace of Spades)
Garrett states that
Truman was never endangered by the assassination attempt. Collazo and Griselio never made it inside Blair House, thanks to Coffelt and the other White House Police Force officers.
Stephen Hunter, who wrote the book on this assassination attempt, is less certain that HST was never in danger. He believes it likely that Truman was at a window and exposed to Torresola right when Coffelt ended the fight. Had the officer missed, Truman might have been shot. In addition, Hunter doubts that the agent with the Tommy gun was certain to stop the assassins had they made it into the residence.
That is all the more reason to honor Leslie Coffelt: a man who did his duty as his life slipped away.
I discussed Hunter's book here.