No, the event that will be cited as the primary cause of the decline and fall of the US will be the Immigration Act of 1965. It set the stage for what has happened later.
I suspect that you're correct, but other factors of the mid-60s will get blame. The VietNam War did not have the clarity of purpose of earlier wars, thus we wouldn't have even known if we did win. Eisenhower warned us of the "military industrial complex" ever striving for more power and control. His presidency does not get the credit he deserves. Technology has had its plusses and minuses.
Which one's irreversible? That would be that immigrants before that time mostly came to the US to work hard and achieve the promise of America. Too little assimilation and too little separation from the rest of the world blurred that.
A went to my 50th HS reunion last summer. It was bittersweet. The people I grew up with are fantastic, many of our dreams fullfilled in life. But for younger generations? It's not the same world.
I ramble. I don't think the promise of the US can be salvaged and brought back to our original exceptionalism. But just as the Roman Empire did, we'll fall, a large part of the culture will be preserved, and some newer, smaller, smarter countries will emerge.
Look at Russia. Is what emerged smarter than the empire that fell? Does it own the future? Who knows?