Maybe I'd refer you to the House Committee on Un-American Activities or the anti-communist investigations of Joe McCarthy. But there are probably older examples than that. Putting an official veneer on a baseless conspiracy theory for political gain is not a new trick.
Good example. So, why do we even entertain conspiracy bs? If Eisenhower and people who knew better actually confronted McCarthy and cut off his bs early on, McCarthyism wouldn't be part of our history.
If I remember my US history, good people like JFK's younger brother, Robert Kennedy, at the time a recent Law School grad, future President JFK's AG, and the leading Dem presidential candidate in 1968, was on McCarthy's team. McCarthy was finally censured by the Senate in 1954; John F Kennedy of MA, ostensibly recuperating from back surgery, was the only Democrat not to vote in favor of the measure