There is essentially no possibility of squeezing this kind of money out of the existing manned programs. There can't be any significant scale back in Shuttle or Station in the FY05-09 time frame, because we will still be assembling the Station. Possibly there will be some small reduction in the Shuttle flight rate from the former 5/yr. But as NASA never tires of mentioning, cutting back the flight rate of Shuttle doesn't save a lot because the marching army of support people have to be kept on salary anyway. Implementing the CAIB recommendations will increase cost and staffing levels, not reduce them. Maybe they can save some money by letting VAB and the rest of LC-39 decay away, but not very much.
So there is really no alternative to cutting over $2B/yr out of the non-manned-space half of NASA's budget. That's a ~%35 cut if you assume it is equally distributed over the five years 2005-2009!! If it is ramped in like most big budget cuts, the final cut by 2009 would be much larger. Goodbye aeronautical research, goodbye Webb Space Telescope, goodbye planetary probes to boring places like asteroids.
Do we really want to trade all this in for Apollo Mark II? A lot of people will say no. Even a lot of Space Cadets will say no. We lost ten years of solar system exploration to pay for the Shuttle and it left a bloody wound that still drips. A lot of influential people will fight this proposal to the last round, and then fix bayonets and keep on fighting until it is defeated.
The Shuttle was cut to the bone throughout its development and the tragedies that followed reflect that. Cutting it further is literally impossible if any shuttle is ever to fly again. Abandoning the Shuttle would mean abandoning the International Space Station as well. Bush I proposed a similar plan at a cost of US500 billion. I have not been tracking US inflation since 1989 but I doubt it has deflated half a trillion dollars to just over one hundredth of a trillion dollars.
The Bush plan, then, is (surprise!) a severe budget cut to the unmanned space program, far the most productive NASA activity, in favour of a goal that can only succeed at least 7 years after Bush leaves office (if he is re-elected next year). I hesitate to call a space program so much air, but what choice do I have?