Rush Limbaugh, the conservative talk-radio pioneer, has been called many nasty things before, but never a "structural imbalance." That's the fancy term a liberal think tank uses to characterize his success -- and to dress up its proposal for counteracting that success through new government regulation.

The report of the Center for American Progress on "The Structural Imbalance of Political Talk Radio" marks the latest phase in liberaldom's grappling with conservative talk radio. First came the attempts to create a liberal Limbaugh -- Mario Cuomo, Jim Hightower, et al. -- that fell flat. Then an entire left-wing network, Air America, was founded, and foundered. So there's only one option left -- if you can't beat them, and you won't join them, you can agitate for government to regulate them.

The report looks at a slice of 257 talk stations and concludes that more than 90 percent of total weekday talk programming is conservative. The supposed reason for this is, essentially, that media companies are conspiring to shove conservative radio down the throats of listeners in a way they couldn't if, among other things, government required broadcasters "to regularly show that they are operating on behalf of the public interest."

This is a pinched view of radio. There are upwards of 2,000 talk stations in the country that deal with news and issues, according to Michael Harrison of Talkers magazine, and they encompass all sorts of formats from National Public Radio to urban radio to shock jocks, none of which are dominated by right wingers. Conservative talk radio is a vibrant niche within that market, but there are many other places to go for news and opinion.

What is hard to find are liberal replicas of Rush Limbaugh, and that is due to the deepest structural imbalance of all -- talent. Limbaugh and other top conservative talkers are silver-tongued, informative and -- importantly -- entertaining. These are qualities that can't be conjured out of nowhere, and designated liberal-radio saviors have tended not to have the requisite talent "on loan from God" (as Limbaugh puts it).

There have been conservative failures at talk radio for the same reason. Without the right mix of substance and entertainment, a host will fail to get ratings, and with that, be yanked from the air. "Ratings" is a word that appears only once in passing in the Center for American Progress report, because then it would have to acknowledge that conservative radio is successful exactly because it gets listeners.

Broadcasters go where the money is. If a liberal could draw the kind of listeners -- and hence the kind of advertising dollars -- as Limbaugh, he too would be on more than 600 stations. This is why Spanish-language radio is such a growth commodity. Not because broadcasters have an agenda to Hispanicize America, or because there's a structural imbalance that favors Spanish-language over German- or French-language programming, but because there's an audience for it.

The Center for American Progress wants to short-circuit the market. Having bureaucrats determine whether radio stations are serving the public interest is inherently dangerous. There are times -- like now, in the debate about the immigration bill -- when Democrats and Republicans in Washington will agree that conservative talk radio is not serving the public interest because it brings to the table public sentiment that the establishment prefers to ignore.

The report avoids directly calling for a renewal of the constitutionally dubious Fairness Doctrine that mandated equal time for conservative and liberal opinions, although some Democratic lawmakers aren't so circumspect. After five years of opposing most assertions of government power to fight terrorism, these liberals are ready to wield it to fight conservative talk radio. After maintaining that the First Amendment protects nude dancing, they are ready to argue that it doesn't quite apply to people broadcasting conservative views over the airwaves.

In our toxic contemporary politics, it's a sign of success if you drive your opponents batty. Rush Limbaugh might be a structural imbalance, but his critics appear simply imbalanced.