I tentatively suggest it started rather rearlier and has (_merely_) hardened. Starting dates could be August 8, 1945, or the Marxhall Plan or the launching of The Great Red Scare under Truman or the Taft-Hartley Bill, with its prohibition (unchallenged by labor) of Secondary Boycotts. Without the weapon of the Secondary Boycott Labor _as a Movement_ essentially disappears. Looking back from Trump what we see is a partly spontaneous, partly conscious and systematic Counter-attack by Capitalist elites on the gains labor had made from 1917 to 1945. I would sggest Kennedy's Inaugural Address as systematizing that counter-attack (Back sometime in the '70s, either in personal conversation or in some paper, Bruce Frandlin pointed out that "the 60s" left was the first left not grounded in and supported (actively supported) by The Labor Movement. Taft-Harley had succeded: Repression worked.
I would like to see another crude summary & analysis of history 1945-1988. I'm suggesting that Reagan-Thatcher represented not the biginning but merely the formalization of that post-war offensive by capital.
Carro
P.S. In some moods I would assert: The Class War is Ended -- Capital (Barbarism) is triumphant.