As you frame it, as valid a pontification as mine. But different vantage.

You're addressing the utopian Hopes of a Class.
My generalization, placing June 1968 as Inflection Point for the subsequent (mostly-uninterrupted) curve of 'National Decline' tries to average the effects (emotional + intellectual) ...
on so-many observed: of That RFK assassination, as culminated the trio, since 11/63.

(I postulate that, RMN made it to the WH ONLY because there was no longer an RFK to oppose (and I say: trounce) him.)

Agreed: 'National Decline' / '1968 Elections' (including the Chicago Police riot, etc.) all are open to personalized versions/definitions of the matters. Inescapable that.
Yet, by various measures: it Has Been a [-]-Slope on the Y-axis, since mid-1968. qed