Editor's note: David Frum writes a weekly column for CNN.com. A special assistant for President George W. Bush from 2001-02, Frum is the author of six books, including "Comeback: Conservatism That Can Win Again," and the editor of FrumForum.

Washington (CNN) -- After NPR fired analyst Juan Williams, Sen. Jim DeMint sent this tweet to his Twitter followers:

"The incident with Juan Williams reminds us the only free speech liberals support is the speech with which they agree."

Maybe so. But if DeMint, a Republican from South Carolina, meant to imply that conservatives have a better record, then I have two words to say to him: Brink Lindsey.

Brink Lindsey is not a household name outside the Beltway, but inside he's a well-known writer and thinker. After a successful career as an international trade lawyer, Lindsey was hired by the libertarian Cato Institute. At Cato, Lindsey studied trade issues, wrote two widely praised books, and launched the institute's influential web magazine http://www.cato-unbound.org/ He was promoted to Cato's vice president for research.

"Libertarianism" is a philosophy of personal freedom that fits awkwardly within the American party system. Yet by and large libertarians have tended to align themselves within the Republican political coalition. Certainly Brink aligned himself that way through most of his adult life: I know, because he and I have been friends since we attended law school together back in the 1980s.

Brink initially supported the Iraq war. But as the war soured, Brink soured on the leaders who had waged that war. Brink began to argue that libertarians might find more natural partners in the Democratic than the Republican party. So long as George W. Bush remained president, Brink's Cato colleagues remained open to Brink's anti-Republican views. Lindsey received funding to start a private series of discussions to explore liberal-libertarian commonalities. (Disclosure: Although neither a liberal nor a libertarian, I attended one of these discussion sessions).

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All proceeded in a thoughtful think-tank way until the election of Barack Obama in November 2008.

For libertarians and their donors, the election of Obama threw open all the terror of the advent of the apocalypse. Discuss ideas over dinner with Obama supporters? You might as well break bread with emissaries of Satan.

As with Juan Williams, there came with Brink a straw that broke the camel's back:

Lindsey published a negative review of a new book by Arthur Brooks, president of the American Enterprise Institute. Brooks argued that America was riven by a radical culture war, with 30 percent of the country manipulating democratic institutions to impose European-style social democracy on an unwilling 70 percent majority.

Writing in the liberal (uh oh) American Prospect in July, Lindsey argued:

"Figuring out how to restore growth and how to construct an effective but affordable safety net, are questions for debate, analysis, and democratic decision-making. My answers to those questions may differ from yours, but dividing up into warring tribes and demonizing each other aren't the ways to figure out who's right."

Shortly after that article appeared, Lindsey was fired along with a more junior Cato associate with whom Lindsey was co-authoring a book, Will Wilkinson (now a blogger at the Economist).

Neither Lindsey nor Cato have any comment on the separation, but see here for my reporting soon after the event.

The Lindsey-Wilkinson firing touched off no Fox News explosion. No bold assertion of the principle of freedom of expression: only a little murmuring among Washington policy elites.

Among the right-wing of that policy elite, the murmuring was especially nervous. The Lindsey-Wilkinson firing followed my own termination from the American Enterprise Institute in March, after I posted a blog item lamenting that Republicans had thrown away an opportunity to negotiate a health care deal in order to inflict a personal defeat on the president. Which termination in turn followed the firing of Bruce Bartlett from a Dallas-based conservative think tank after a book criticizing the Bush administration for overspending.

Sometime before these events, a young Cato Institute blogger named Julian Sanchez proposed the term "epistemic closure" to describe what was happening in the conservative world. That's a fancy way of saying that minds are closed to contradictory information.

And one demonstration of how minds are closed? The ability to raise a howl about liberal close-mindedness after the firing of Juan Williams -- without recalling one's own side's exactly comparable actions not even 90 days ago.

The opinions expressed in this commentary are solely those of David Frum.