I was a Scoop Jackson Democrat. I heckled Soviet speakers in college when kids my age were going to anti-Vietnam War demonstrations. I opposed the Vietnam War on the grounds that we were screwing it up so bad we had no chance of winning & so should cut our losses & get out, not because I thought it was wrong or had any illusions about Communists.
As an example, the final exam for Stevenson college's spring 1968 core course, Stability & Change in the Soviet Union, asked what the USSR would do about Prague Spring. I predicted in May that the USSR would invade Czechoslovakia about 10 days before the Democratic presidential convention in Chicago, and gave reasons which turned out to be dead on. This led to an interesting job offer my senior year.
But the Democrats kept moving left after the Vietnam War and eventually started siding with the Communists. I couldn't stand that and switched to the GOP after then US ambassador to the UN Jean Kirkpatrick switched for the same reason.