But if you’re a fan of Mark Levin’s radio show, you’d have just as much cause to believe that Americans for Prosperity, a FreedomWorks rival, was the most effective conservative advocacy group. And, if Rush Limbaugh or Sean Hannity are who you listen to, you’d be hear a steady stream of entreaties to support the important work of the Heritage Foundation.

That’s not coincidence. In search of donations and influence, the three prominent conservative groups are paying hefty sponsorship fees to the popular talk show hosts. Those fees buy them a variety of promotional tie-ins, as well as regular on-air plugs – praising or sometimes defending the groups, while urging listeners to donate – often woven seamlessly into programming in ways that do not seem like paid advertising.