Senator Obama has gone to Hawaii to be with his ill grandmother (We wish her well)
Senator Biden has disappeared off the campaign trail. Rumor has it a noted surgeon is busy trying to remove a Florsheim stuck between the Senator's teeth.
Given what's transpired the last few days, perhaps they think silence is golden. In football terms, they are now running the prevent defense http://en.wikipedia.org/wiki/American_football_strategy#Prevent
Sitting back in a deep zone usually avoids sudden scoring passes or damaging penalties. But take it from someone who has cringed every time the NY Giants adopt this ploy when they hold a late lead, it's also a great way to lose in the last minute of the game.
As noted philosopher John Madden once said:. All a prevent defense does is prevent you from winning.