Nancy Pelosi objects to Mitt Romney's "Mute Button" ad.

Because she would never ever put any President on mute.

"As speaker and as Democratic leader, any call from the president would be treated with great formality and respect," Pelosi said. "There was absolutely no situation in which either President Bush or President Obama were cut off from speaking. I respect the office of the President and the office of the Speaker, including the historic nature of any communication between these two offices."

Here's the ad, which gets its assertion of fact from Bob Woodward's book:

ADDED: A possible middle ground is: Pelosi had a button that kept the sound at her end from passing through to the President. His voice would still be heard, and he would never be cut off, but she would be free to talk over him and have conversations with whoever was with her. That would make her statement completely true and — ah! I just checked the book text — it would make Woodward's reporting precisely accurate:

Pelosi reached over and pressed the mute button on her phone. They could hear Obama, but now he couldn’t hear them. The president continued speaking, his disembodied voice filling the room, and the two leaders got back to the hard numbers.

Woodward never said she muted the President, and Pelosi's starchy outrage does not include a denial that she muted herself.