I have to think America peaked in the early sixties.
My belief also..I think it all started unraveling on 22 Nov, 1963.
Many of the infected college grads went on to become leftist college profs and hs teachers further infecting another generation with leftism. And that is where most of the increase of leftism is generated today. The leftist hs and grade school teachers.
Even the Dem Party and its members and voters were fairly patriotic in the sixties. That started to change drastically with the nomination of George McGovern in 1972. A leftist like McGovern could never have been nominated in 1960. His nomination, even though he got killed in the general election, signaled a huge shift in the sentiment of many Dem voters. Leftists now ran the party.
The plague of leftist has increased mightily since then with no signs that the plague has diminished. Who knows where it will end. The dissolution of the country split between leftists and conservatives? Not out of the question now.