Why does President Obama have two microphones on his lectern when he speaks.

Why does President Obama have two microphones on his lectern when he speaks? Why not just one? Is one for PA and one for the press? Is the other one just for a backup or for better sound? Why two?

one is for us, the other is for the stenographer.

One microphone is on, and the other serves as a backup. Both lead to a distribution box from which everyone gets their audio feed (the room's speaker system, news agencies, etc). This is because security policies involving the President require controlled sterility of everything around him, such as to prevent a microphone-shaped bomb to get emplaced right in front of his face.