The President is walking out of the White House and heading toward his limo, when a possible assassin steps forward and aims a gun. A secret service agent, new on the job, shouts "Mickey Mouse!"
This startles the would be assassin so much that he hesitates and as a result is captured.
Later, the secret service agent's supervisor takes him aside and asks, "What in hell made you shout Mickey Mouse?"
Blushing, the agent replies, "I got nervous. I meant to shout......
"Donald, duck!"