This bears repeating. The government will spend $4 trillion this year. Less than one half of one percent will go to an agency that expands our knowledge, improves our lives, monitors our environment, and helps us look beyond our current troubles and see our future as a species. Oh, and provides high-tech jobs and countless other benefits.
Paradoxically, the visibility of NASA's Mars rovers, space shuttles, etc., leads the American people to think a large portion of the national budget goes to the agency. NASA also has to deal with idiot remarks by people like Katie Couric, who said in 2006, "I can’t help but wonder what all the money could do for people right here on planet Earth." Katie, where exactly do you think it's being spent? Are the rovers carrying away cash to pay off Martian contractors?
Think about your idol, Walter Cronkite. Walter understood what we were doing and why it was worth it.
Space exploration is much more than just NASA, and I'm certainly not holding NASA up as a perfect agency. But think about it. One half of one percent. It's not enough. Given all the missions the agency is tasked with, it's not even close.