Nixon in the HospitalVideo of VP Nixon in the hospital being visited by then President Eisenhower. This was just prior to the first of the 1960 debates and caused Nixon to show up to the debate underweight, underprepared, and sickly.
History Channel - This Day in HistoryThe History Channel takes a brief look at the First Kennedy-Nixon debate. This is good for a summary. The video starts discussing the impact of the debate at the 00:34 mark.
Two minutes of actual footage from the debateThis footage is good because it shows the difference in appearance between Nixon and Kennedy. Also you can see how much more seamless Kennedy's response is - not necessarily in content, but in delivery.