It doesn't matter whether you could "prove" to what extent an election was affected by the disinformatia, hacking, Wiki releases and possibly yet-to-be-discovered facets of an organized propaganda, dis- and mis-information campaign.
From posts I see in this forum, too many Americans are naïve about the underlying literature, project development and strategies or psy-war campaigns conducted in other countries with measurement instruments to gauge success.
Between 1945 and 1960, The US government and mostly the CIA spent billions annually on grants to sociologists, psychologists, and other disciplines for secret research in mass communications and the dark arts or science that had a foundation in the ideas of Goebbels and Harold Laswell. Think about parallels to Werner von Braun in the space business, but in these other disciplines. They'd sit in an office, publish papers in Public Opinion Quarterly, and write their classified work for the grants.
Some time after there arose a confusion of CIA projects on American soil, there were congressional investigations revealing things that wouldn't be declassified to the public until decades later. Those projects were closed down. Of course, if a Hollywood director with a spy movie project needed to consult with the careerists at Langley, and if he wanted footage of the Langley building interior, there's a possibility just for instance that a doctrine or worry about the agency itself might transmit an impression of characters that would prove historically contrary.
So you might see it in a film like Yuri Nosenko KGB produced about 5 years before they finally caught Aldrich Aimes.
There are CIA manuals [no less, KGB compendiums] on the topic dating probably back to the 1950s. But if anyone had been the master of it, they would master it most successfully in a totally pluralistic media market. One could compare that with the old USSR -- a place where everyone knew where the information was coming from, and enough would figure out whether to take it seriously. But in an atmosphere of limited state-run media, there was no challenge to the craft of the psy-war specialist.
Apparently, they have caught up.
Look up the expressions "misprision," "misprision of a felony," "misprision of treason." Foreknowledge, add complicity, coordination, cooperation, or collaboration. With a foreign power, for instance.
Painful holiday for everyone. Some just think it might have been avoided with less of the ingenuous citizen.