NASA administrator Michael Griffin testified before the Senate Committee on Commerce, Science and Transportation on 28 February 2007, saying that recent budget cutbacks could push the first Project Constellation missions into 2015, increasing the gap between the Shuttle and Orion programs.
We don’t want to wind up without manned spaceflight capability, like we were between Apollo and Shuttle! Let’s go, Congress - someone will colonize the moon and Mars, it might as well be us!