Donald Trump 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 and he is captured.
Later, the secret service agents supervisor takes him aside and asks,

What in the hell made you shout Mickey Mouse? 

Blushing, the agent replies,

I got nervous. I meant to shout Donald, duck!