A Guardian report "US elections: McCain married to first wife when he applied for licence to marry second, report says " adds one more fact to the story of how Cindy got the captian.
It notes that the senator told his biographer that there had been a series of others before the beer heiress.
Excerpt:
In the late 1970s, McCain was a US navy captain when his marriage to Carol, a former model who was nearly crippled in an auto accident during his captivity in Vietnam, began to fall apart. He later told his biographer, Robert Timberg, that he had engaged in a series of extra-marital "dalliances".
The main gist of the Gurdian report was the fact that John and Cindy pulled their marriage license before his divorce was final from his first wife. Though some sites are talking bigamy, I don't think a license constitutes a marriage until finalized which the happy couple did in May, though checking the current rules for an Arizona marriage license at marriagelicense.com does point to a problem there.
If either applicant has been married before, you may be required to bring Proof of Dissolution.
I guess that a bit of 'walking around money' was good enough "Proof of Dissolution" for the clerk who issued that license.
As to why the couple made the preemptive license pull, I'm guessing that Daddy Hensley said something about 'intentions', or maybe he'd gotten wind of the navy captain's previous flings.