One main "corrupting influence" named by Swanson (Prosperity Agenda, 9/2/09) is

corporate media, which had always whited out single-payer and eagerly aired lies and distortions about the public option, moving the center of the debate somewhere to the right of that proposal. This is not--I repeat, not--because the right-wingers are smarter or wittier or more disciplined. It is primarily because the corporate media shares their agenda, no matter how sloppily or inarticulately they present it. The media companies share board members with the health insurance and pharmaceutical companies, not to mention selling them advertisements. There is no more common excuse for hesitancy from progressive congressmembers than "But the media would attack me."

See FAIR's magazine Extra!: "Single-Payer & Interlocking Directorates: The Corporate Ties Between Insurers and Media Companies" (8/09) by Kate Murphy.