I would think the release of the Zapruder film in the early 70s . . .
Which shows seven primary witnesses (including JFK, Jackie, and JBC) to Oswald's first, missing-everything shot at "Z-124" consciously reacting to it between frames Z-140 and Z-150, which shows JFK's and JBC's nearly simultaneous reactions to being hit from behind by CE-399 at approximately Z-222, which shows at least two of JFK's skull fragments flying in a forward direction, and which shows most of JFK's blood and brain matter being propelled forward.
. . . the Pentagon Papers
Which, ironically, Kremlin-loyal FEDORA's telling Hoover and Nixon that the Kremlin had a complete copy of (it didn't) caused the latter to set up . . . wait for it . . . The Plumbers!
. . . and the Church Committee hearings
During which James Angleton testified about KGB Colonel Nikolai Leonov (aka "The Blond Oswald in Mexico City") and said that the guy at the Soviet Embassy who volunteered the Department 13-radioactive name "Kostikov" to a forgetful Oswald (or a "forgetful" Oswald impersonator?) over a sure-to-be-tapped-by-CIA phone line on 10/1/63, Ivan Obyedkov, was a Kremlin-loyal triple agent, i.e., whom the CIA mistakenly believed it had successfully recruited
. . . just to name a few things, certainly contributed - rightly so - to a general feeling of distrust of government in the "national psyche " long before Oliver Stone.
Bummer, dude.