All that coughing and hacking on the campaign trail would be visible evidence, this sickly grandma, is not physically able to continue her dedicated (to the American people, of course) drive for the Presidency. Or, a sickly spouse (many have witnessed Bubba's deteriorated appearance on campaign stops, in front of non-existent crowds) could force Hillary Rodham to stand by her man, and terminate this now insignificant Presidential run. Obviously to look after her ailing husband. (Insert 'Tara's Theme here)
It is as simple as that.