According to this NYTimes article, General Clark has actually brought Einstein’s theory of relativity into the Presidential campaign.
Well…maybe not exactly as a campaign issue, but in a “discussion of NASA’s future at a recent gathering in New Hampshire” Clark said, “I still believe in E=mc2, but I can’t believe that in all of human history, we’ll never, ever be able to go beyond the speed of light.” He further described this as his “only faith-based initiative.”
The NYTimes article further explains why time travel might not be entirely outside the range of Einstein’s theory.