"Reports that say that something hasn't happened are always interesting to me, because as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do no know. But there are also unknown unknowns -- the ones we don't know we don't know

We've got a very serious problem, ... Wolf Blitzer Reports.

There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don't know. But there are also unknown unknowns. There are things we don't know we don't know.

Enjoy your time in public service. It may well be one of the most interesting and challenging times of your life.

That's what happened, notwithstanding any cell phone reports to the contrary,

[In Washington, thousands of people marched in remembrance of the attacks and in tribute to troops fighting overseas.] I wish we could say ... that we were gathering today to commemorate a danger that had long since past, ... But we cannot. The enemy, though seriously weakened and continuously under pressure, continues to plot attacks, and the danger they pose to the free world is real and present.