Although political "flip flopping" is sometimes condemned as if it were a crime, let's face it - politicians are always adjusting their positions and sometimes even reversing them. Situations change, new information and analysis becomes available, mistakes are made, strategies are changed. If there's a good reason to change a position, and if the candidate can explain and justify it, it's crazy to stick to the original position for its own sake.
This doesn't mean that it's OK to just say whatever you want for the circumstance or the current audience (besides, for a presidential election, the whole world is your audience anyway). Consistency is important, but I think it's most important to be consistent at the big-picture level of what's good for America. Of course if candidates change their positions too much or too erratically, their opponents will point this out, and if those positions are really not workable and good for America, the people will see this too and vote accordingly.
McCain and Obama have both changed positions on issues, and today it seems that Obama has significantly reversed his previous position on space exploration and NASA. He had originally proposed delaying the Constellation program by five years and using the savings to fund an early education program. I disagreed with this position because I believe the savings would be too small to make a difference in any significant social program, and because NASA and its work force are an important national resource that would be difficult to rebuild. Even with the growth in private space (which I believe NASA should be funded to support at a higher level), I believe that NASA's 0.6% of the Federal budget represents a true investment in our future, unlike so many other Federal programs.
Today in a speech in Titusville, Florida that was largely focused on economic issues (according to a community blog on Obama's web site), Obama changed his position and emphasized the risk of the US losing its competitive edge in space capability. He proposed extending the shuttle program by one launch and speeding development on the Constellation program to minimize the gap in US manned space capability. Of course he's talking about jobs in this region, but he had a bigger picture in mind as well:
"More broadly, we need a real vision for space exploration. To help formulate this vision, I’ll reestablish the National Aeronautics and Space Council so that we can develop a plan to explore the solar system – a plan that involves both human and robotic missions, and enlists both international partners and the private sector. And as America leads the world to long-term exploration of the moon, Mars, and beyond, let’s also tap NASA’s ingenuity to build the airplanes of tomorrow and to study our own planet so we can combat global climate change. Under my watch, NASA will inspire the world, make America stronger, and help grow the economy here in Florida."