Maybe I'm slow on the uptake, but I just recently came across the story about Upton Sinclair's 1934 run for California governor and the dirty tricks by the pre-liberal media his potential victory inspired.
Sinclair, the muckraking novelist whose Oil! became the basis for There Will Be Blood, was a socialist running as the Democratic nominee against a Republican party hack. With a program called EPIC (End Poverty in California), Sinclair drew more voters in the primary than Republican Frank Merriam, despite the fact that California was a heavily GOP state.
This disturbed the establishment, which in those days was headed by movie moguls who then, as now, had greater loyalty to money-making than to liberal ideology.
The execs prefigured the threats made by pro sports team owners by threatening to move their studios to Miami if Sinclair were elected, and the Los Angeles Times denounced the "maggot-like horde of Reds" who supported Sinclair. But their most effective measures were mobilizing their marketing and story-telling resources in a disinformation campaign.
To smear Sinclair, experts made innovative use of film, radio, direct mail, opinion polls, phony leaflets and false advertising. The political effort that produced the strongest impact was the manipulation of the movies. For the first time, Hollywood put all its professional and financial resources into action against a Democratic candidate. Led by Louis B. Mayer, a rabid Republican who headed M-G-M, studio executives raised enormous sums of money, intimidated their employees and produced propaganda films.
[...]
The pro-Sinclair forces were pitted against Mr. Mayer's protege, Irving Thalberg, who produced a propaganda film showing bums arriving in California to take away everybody's jobs and cause trouble. Fake leaflets were printed stating that the Communists endorsed Sinclair and branding him a dynamiter of churches and all Christian institutions. Radio scripts warned against the dangers of Sinclairism, saying it would mean higher taxes. A radio melodrama intimated that "Governor" Sinclair would confiscate everybody's swimming pools.
I've only been able to find descriptions of the fake newsreels Thalberg created and ran in California theaters. Cast from the lower ranks of the studios' actors, one featured an "inquiring reporter" asking "people on the street" for whom they intend to vote and why. Bums, morons and anarchists with Bolshevik accents declared themselves for Sinclair. The well-spoken middle class voters were all for Merriam.
Another clip was based on a sarcastic retort by Sinclair to a question about the poor flocking to California to take advantage of his EPIC plan: "If I'm elected governor, I expect one half the unemployed in the United States will hop aboard the first freights for California." The newsreel obligingly showed the deadbeats and dirty Trotskyites massing on the California border, waiting to descend upon the election of Governor Sinclair.
There's much more history of the Sinclair campaign and the opposition's tactics here and in a 1992 book by Greg Mitchell.
But then, I guess you could just watch the news.