There really was a bit flip at the time, though it was more of a return to form. It grew out of McCarthyism and the John Birch Society, which themselves were the phoenixes born of the ashes of paranoia about anarchists and communists from the early 20th century.
And more controversially, I'd trace that to the same arguments as the Civil War and going back before the Revolution.
We seem to have had periods of calm prosperity (post Civil War, post WW II) against a base of xenophobia and internal dissension that goes beyond just ordinary differences of opinion. The late 60s were the end of one of those periods, and it has been an exponential curve ever since. It's all inflection points for over half a century.
I feel like its easy for "Trust, but verify" to degrade into "Verify, then trust". It's that initial step of distrust while verifying that starts to sour things.
Tellingly, Reagan’s America is where I really notice cultural growth dying out and trust vanishing.