Well, as Nixon took us off of the gold standard in ‘71 with the observation “I am now a Keynsian in economics”—anyone who was paying attention. (Not me though—I was learning how to talk.) My Mother says it hit her when watching the results come in during the ‘64 election. Looking back—I’d say no later than Roosevelt’s third term we were headed in the wrong direction with no clear path for turning things around.
That set the table, but LBJs 'Great Society' with both un-capped and unfunded 'entitlements' took us over the top fiscally. (Aside from destroying families)
Yes, I saw it 40 years ago and I was still young and inexperienced. As they say, it's not the fall that hurts... it's the sudden stop. We are getting very close to that thanks to politicians promising everything to people even if there is no way to pay for it for the last 40 years.