I’d add a couple more decades on that, GOP’s degradation roots in 1950s during Eisenhower/Nixon and was later cemented by Nixon/Spiro. The Southern Strategy and “Silent Majority” with increasingly crypto racism were all Nixon hallmarks. Reagan built on them in the 80s and things have only got more extreme with modern right wing media in the 90s of course, but it all roots back to those early post-WWII years when so many things changed.