One thing about Rush Limbaugh: When he steps in it, he steps in it big time. And he sure did so this time.

For El Rushbo, as he proudly calls himself, it started out as a classic Republican Party smear campaign: When you can’t defend your own party’s policy, launch a personal attack against those on the other side. It’s always worked for Rush in the past. As I document in my new book, “The Obama Hate Machine,” Rush is the king of smears against President Obama. He regularly refers to him as “Imam Obama” and the “first Muslim president.” He’s called him an “economic ignoramus” and a “jack–s.” He alone, citing an investigative report by Cat Corben, accused Obama on air of cheating on his wife when he was supposed to be attending his daughters’ soccer game. And he contends that Obama was elected president only because he was black and that, were he not black, he would be nobody today but a tour guide in Honolulu.

Over the years, Limbaugh has directed some of his ugliest attacks against women: branding all feminists as “feminazis,” comparing Nancy Pelosi to a “suicide bomber” and calling the National Organization For Women a “terrorist organization.” And, for a long time, he was able to get away with it – as long as his targets were prominent politicians or celebrities. But this time, he picked the wrong victim: a Georgetown University law student named Sandra Fluke, whose only “crime” was asking to testify before Congress – in support of President Obama’s policy to include birth control as part of every woman’s basic health insurance policy, and against Republican efforts to overturn it.

“What does it say about the college coed Susan Fluke (sic), who goes before a congressional committee and says that she must be paid to have sex,” Rush asked his adoring audience on Wednesday, Feb. 29. “What does that make her? It makes her a slut, right? It makes her a prostitute.”

When, at first, he didn’t stir the kind of controversy he thrives on, Rush doubled down: insisting that if men were going to pay for Fluke and others to have all the “recreational sex” they wanted (you’d think a man who’d been married four times would know a little more about the pill), then men should at least be rewarded in return with videotape of her having sex. That sick comment indeed unleashed a firestorm of outrage and may have triggered the final unraveling of Limbaugh’s long, disgusting and inglorious media career.

By the end of the week, after the first few corporate sponsors had canceled their advertising on his program, Rush was forced to issue an apology. It was perhaps the first apology of his career, and undoubtedly, the most insincere apology ever – driven, clearly, not by any regret for the language he used in attempting to discredit Ms. Fluke, but by fear of losing any more advertisers. But, to their great credit, advertisers were not convinced. They know a phony when they see one. It didn’t make any difference how many times Rush reminded them how much money they’d made advertising on his program, they simply no longer wanted to be associated with America’s merchant of hate. By this writing, more than 40 sponsors had dropped Rush’s program, including such corporate giants as Quicken Loans, ProFlowers, Sleep Number mattresses and Legal Zoom.

The courage of advertisers, however, appears in stark contrast to the timidity of Republican leaders. This could have been Mitt Romney’s “Sister Souljah” moment. Instead, he merely avowed that “slut” and “prostitute” would not have been his “choice of words” – leading Obama adviser David Axelrod to wonder how Romney could be trusted to stand up to Mahmoud Ahmadinejad if he was afraid to stand up to Rush Limbaugh. By their near silence, Republicans signaled either their assent with Limbaugh’s comments or their fear of him. More likely, the latter.

In the end, the market alone will decide whether Limbaugh survives or soon joins Glenn Beck in no man’s land. But the controversy surrounding his unwarranted attack on Sandra Fluke raises again the question of what talk radio is all about. Those of us privileged enough to be given the microphone have the opportunity and responsibility to inform, entertain, involve and maybe even inspire our listeners. Those who use the microphone only to attack and demean others don’t merit the microphone – and deserve to lose it.

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