The party of FDR, JFK and Hubert Humphrey started its death spiral in 1972 with the takeover by the McGovern Demorats. Its deterioration into a party driven only by seething hatred of George Bush is the final phase. I can't imagine why anyone other than those caught up in the Bush hate rhetoric would ever vote for these people.
Started earlier than that: remember the Chicago Convention in '68?
That was the beginning, when they discovered that screaming and shouting could be substituted for ideas, and that (some) good men could be intimidated by bad.
Those that resisted joined the GOP.