Overview: Dr. Sanjay Gupta reports on the toll that serving as president has taken on the health of past commanders in chief. Also: what the medical records of John McCain and Barack Obama reveal about their readiness to serve as president. Included: interviews with former White House press secretaries Ari Fleischer, Joe Lockhart, Jody Powell and Ron Nessen; former Reagan White House chief of staff Kenneth Duberstein; and former White House physicians Rob Darling, Burton Lee and Connie Mariano.