Sinatra was essentially "born" a Democrat. His brash, foul-mouthed and aggressive mother, Dolly, who campaigned for Al Smith, was a Democratic Party ward boss in Hoboken, New Jersey.
Of course, the singer's affiliation with, and support for, John F. Kennedy before, during, and after the 1960 presidential campaign (against Richard Nixon) is the stuff of legend. According to my personal Sinatra "Bible," J. Randy Taraborrelli's, Sinatra: Behind the Legend, during 1960, "...Frank Sinatra continued his diligent campaign for Kennedy with performances and donations and also by hiring a private investigator to see what kind of dirt he could dig up on Richard Nixon, which, as it would turn out, was not much" (p. 230).
The caption for this Life magazine photo, taken in Beverly Hills, 1960: "Singer Frank Sinatra talking with Edward M. Kennedy (Center R) at 'Key Women for Kennedy In California' rally."
Ha, ha, ha - I wonder if Judith Exner was there?
Sinatra would stump for Hubert Humphrey in 1968 (against Richard Nixon). But by Thanksgiving of 1971, it would appear a political shift had occurred, as he "played host for three days to Spiro Agnew and his family...Sinatra and Agnew had forged a close friendship; in fact, Sinatra was determined to see Agnew president in 1976..." (Taraborrelli, p. 390). The "official" cause for Sinatra's political about face was Richard Nixon's position on admitting China to the United Nations, an issue about which he agreed and had been vocal. So, although "he had been extremely critical of Nixon in the past, Sinatra would now become his strongest supporter, contributing $50,000 to his campaign for reelection in 1972...Many of Frank's friends were angry with him for supporting Nixon and the Republican Party" (Taraborrelli, p. 391).
So, I suppose the world has China to thank for the following marvelous, live Sinatra performance (the original point of the post, I swear to goodness...). He was invited to sing at the White House when the Italian prime minister, Giulio Andreotti, visited in April 1973. The video features the singer doing the Nelson Riddle arrangement from The Concert Sinatra (1963) of "I Have Dreamed." This was during Frank Sinatra's brief "retirement" period and proves he hadn't yet lost his pipes (see 2:17 onward). Nixon is supposed to have said afterwards: "Once in a while, there is a moment when there is magic in the room--when a great performer, singer, and entertainer is able to capture us all. Frank Sinatra did that tonight." But Nixon was known to lie from time to time, so don't take his word for it, see for yourself:
UPDATE 5/2011: Video is gone, I'm afraid. Couldn't find a replacement. :(
Will fix it as soon as I can.