Rush Limbaugh talks with guests in the East Room of the White House in Washington, January 13, 2009. (AP Photo/Ron Edmonds)

Rush Limbaugh’s show has never sounded so bleeding-heart liberal as it did this week, when commercial sponsors bailed and were replaced by the United Negro College Fund, Feeding America, the US Department of Health and Human Services and other nonprofits and governmental agencies. In fact, of the eighty ads running Friday on the online stream of Limbaugh’s flagship station, WABC in New York, seventy-one were public service announcements and three were station promos. According to Media Matters, one of the six remaining paid ads was from an advertiser who had asked for it to be pulled.

Now some fifty national advertisers—more if you count locals—have pulled their ads from Limbaugh’s show to avoid being associated with his attacks on Sandra Fluke as a “slut” and “prostitute.” Rushbo is so radioactive right now that even some PSA freebies are running away from him. The American Heart Association wrote in an e-mail to Bloomberg.com, “It is our practice to be a content-sensitive advertiser, and in light of the current controversy, we will be asking WABC to no longer utilize these unpaid PSAs.”

So it’s been a bad week for Rush. Though maybe not quite as bad as CNN, MSNBC and some blogs have made it sound. They all reported that on Thursday WABC suffered more than five minutes of dead air time where ads were supposed to have run on Limbaugh’s show, leaving the impression that radios across Gotham fell into real radio silence.

But it wasn’t quite as simple, or as satisfying, as that. The five minutes and thirty-three seconds of dead air (distributed over four commercial pods in the three-hour show) occurred, as Media Matters reported, only on WABC’s online show, not on the station’s broadcast.

The dead air, however, was indeed caused by the flight of Rush’s sponsors. Explaining what happened, one radio insider told me, “If advertisers are asked to pull [that many] ads, the system is experiencing something it hasn’t experienced before.” That is, the software’s algorithms couldn’t handle the replacement of so many regular spots with PSAs in the time before transmission.

I asked Michael Harrison, publisher of the trade magazine Talkers if this was the largest exodus ever of radio advertisers. “It’s hard to rank because it’s hard to say how long it will go on,” he says. But in terms of that many advertisers bolting in so brief a period, he says, “This is the biggest.”

“Here’s what matters: how many listeners start to pull out,” Harrison continues. “Then there’s a problem for the future. We suspect that his audience is increasing now. The irony is that Limbaugh’s advertising is probably worth more than ever. But unless you believe that the American advertising industry has a high bar for standards and taste, then there will [eventually] be more advertisers coming on. We’re talking about nobody advertising on the number-one show in the business. How likely is that?”

Harrison, who describes himself as politically neutral and interested only in the health of the broadcast industry, adds, “The worst thing that could happen is that advertisers will gang up on Limbaugh and he’ll end up on satellite or streaming only. If this accelerates to where it severely hurts Limbaugh and thereby all of terrestrial radio, including many stations that play liberal hosts, it will be another nail in the coffin of terrestrial radio.”

But for now, at least, Limbaugh’s stain appears to be spreading mainly to other right-wing talkers (as well as some of the cruder shock jocks). Some ninety-eight advertisers have asked that their ads appear nowhere near Limbaugh, Hannity, Beck, et al., according to Radio-info.com. The website published a memo from Clear Channel subsidiary Premier Networks that listed advertisers (including Ford, GM, Toyota, Allstate, Geico, Prudential, State Farm, McDonald’s and Subway) who, as the memo states,

specifically asked that you schedule their commercials in dayparts or programs free of content that you know are deemed to be offensive or controversial (for example, Mark Levin, Rush Limbaugh, Tom Leykis, Michael Savage, Glenn Beck, Sean Hannity). Those are defined as environments likely to stir negative sentiment from a very small percentage of the listening public.

Of course, if it really was so very small a percentage, this would not be a big problem for talk radio. And Rush would not be spending so much of the time on his program raising support for the United Negro College Fund.