[Captain Peter Blood]

Frank was a Democrat at one time. After the fiasco with Kennedy not coming to his Palm Springs home for New Year's in 1962 Frank was turned off of Democrats and eventually became a Republican.
Frank was a close friend of the Ronald and Nancy Reagan and if you remember put on the Inaugural Gala for Reagan when he became President.
So Frank changed and left the Democrats behind.

[Rastus]

There's a book available that collects letters written to and by Ronald Reagan. There are several from Sinatra, and his support for the President was deep. I'll have to look and see if there's anything in there from Dean Martin.