One of the things about the White House is that you know from the moment you walk in there that this has a time limitation. You don't know exactly what it is; it may be the four years you were elected for, or death, but you know it's got a time limitation. And that's one reason why you do as much as you can do, because you know that this will never happen again, and you can drum up the energy from somewhere within you to go more, do more, learn more, for this limited time.