The reason why the country club crowd so rapidly and easily became Democrat is neoliberalism. In the English-speaking world, neoliberalism was initially championed by conservatives. Thatcher, Reagan, etc. (Not so in Spain, for example, where neoliberalism was brought in by the Socialists).
Wealthy people are by definition those who are doing well in the neoliberal economy. They feel comfortable in it. So they vote for whichever party is more neoliberal. The parents voted Republican when Republicans were more neoliberal. Their children now vote Democrat because the Democrats have become the standard-bearers of neoliberalism.