Define 'fitness'?

Bush Questions Edwards's Qualifications for Top Job (washingtonpost.com)
MORRISVILLE, N.C., July 7 -- President Bush on Wednesday questioned the fitness of Sen. John Edwards to assume the presidency, lashing out at the North Carolinian on his home turf just 25 hours after he joined Sen. John F. Kerry's ticket.

And Bush was fitter to assume the Presidency than Edwards is the Vice-Presidency because.........?