It was a gradual process spanning years, Pat.
Nominal tax rates topped 70% in the 1970s; it had been a time of a long-term moribund economy.
Economists showed us that if we gave the rich a huge tax break, they'd invest it in the economy, making it grow. It sounded promising, so I supported Ronald Reagan. The economy did seem to grow, but the budget deficits grew astronomically to a scary, unprecedented level.
At the same time this was happening, the Religious people took over the Republican Party, and weren't shy about telling the moderates to "get out". Then when the AIDS crisis came, they openly laughed and mocked the gay community, calling us "sodomites who got what they deserved". "AIDS was God's way of getting rid of the 'faggots'", they said.
Then Reagan began the process of de-unionizing the country. With a country left that was full of minimum wage workers, who was supposed to buy the goods that the rich people were supposed to be producing, with all those tax cuts they'd been given?
All these factors put together made me realize that trickle-down economics didn't work, and what was going on with the Religious Right pretty much cinched my departure from the party.
I've never looked back since.