I agree that it started much earlier...however, it has become more pervasive than ever before. These more radical elements were often kept in check, relegated to the fringe by many of their own party faithful.
What we see today, is a party faithful that is embracing this element. I never thought I would see the day that Michael Moore would be a guest, sitting next to a former Democrat president at a nationally televised convention. While these elements did exist in the past, they weren't paraded out front like they are today.
"however, it has become more pervasive than ever before."
No - it was worse back then but now, the MSM no longer has a monopoly and we just know of it better.
Back in the 30's, there were newspapers that were not towing the marxist line. They were showing the millions being killed by Stalin in 1932. The Hearst papers were one group but he was hounded to death and ridiculed by the intelligentsia - e.g. "Citizen Kane", the "greatest" movie of all time.