Something is going down – way down, underground – on the North Lawn of the White House. It's a big construction project, but no one will talk. Refurbishing the bunker? Missile silo? White House Metro stop? Digging for Jimmy Hoffa? So far, the administration is responding with the usual transparency. Before Robert Gibbs took his final bow, the intrepid Mark Knoller of CBS News tried to draw him out on the mystery: Q: And before you leave, can you tell us what they're really digging out there on the North Lawn? Gibbs: I told you, they're moving the monument. It's...