Why will the troop surge in Iraq work?

Oh, this is gold. From AMERICAblog,

PELOSI: He's tried this two times — it's failed twice. I asked him at the White House, 'Mr. President, why do you think this time it's going to work?'

BUSH: Because I told them it had to.

PELOSI: Why didn't you tell them that the other two times?

I'm very interested in how Bush responded to it.