At one time, Republicans were liberal and Democrats were conservative; when did this reverse?

Because in before that the conservatives did not want the middle cl liberlas increasing power because that would be a direct threat to their power. But then in the 1960's the fear of communism escalated that it was also a little too late for conservatives to shut down the liberal middle cl movement, so in the 1960's their job became to shut down communism by going against the working cl.