The Passage of Power (2012)
LBJ's experience in World War II was of a "behind the scenes" sort; he spent a total of 13 minutes in action as an observer on a plane in the Pacific. As Senate Majority Leader, LBJ wore a silver star pin on his label, and regaled his colleagues with his WW II "experiences". In reality, this self-proclaimed "Tailgunner" was an intelligence officer who debriefed pilots behind a desk. JFK was a "Millionaire Playboy" Congressman, and then Senator, who lived lavishly, but was a decorated WW II hero. JFK basically phoned-in his duties as a member of Congress; no serious legislation bore his name in his nearly decade-and-a-half as a Congressman/Senator . . . but there were physical & political reasons for doing so.
JFK had very serious health problems, including chronic back trouble, as well as Addison's Disease. Part of the reason why JFK wasn't a constant physical presence in the Senate was that he had two major back surgeries; upon his return to the Senate in 1955 after an almost two-year absence, the views of his colleagues towards him remained unchanged. Despite his relative lack of import in the Senate, JFK almost became Adlai Stevenson's Vice-Presidential candidate in 1956, being narrowly edged out on a floor vote among delegates by fellow Senator Estes Kefauver.
Below: The 1956 Democratic Convention Vice-President Nomination Ballot
Below: JFK, early in his first term as Senator, talks about US involvement in SE Asia
Cortisone injections saved JFK in terms of stopping the immediate effects of Addison's Disease - he gained weight and energy, while his yellow skin was passed off as a nice sun tan. However, those same life-saving injections actually made his back far-worse . . . JFK, before he even pursued the Democratic nomination for President in 1960, was in very bad physical condition. In addition to his physical state being a limiting factor in terms of his workload in the Senate, JFK also saw being an obscure Senator as a drawback to pursuing the Presidency, so he spent as little time in the Senate as possible, choosing to focus on the upcoming Democratic primary elections.
Below: JFK addresses an audience in Wisconsin on the topic of direct primaries