May 24 (Bloomberg) -- (Update: Five minutes before this blog post was published, Yuval Levin responded to Jonathan Chait at National Review's The Corner blog.)

Kevin Hassett of the American Enterprise Institute did some data collection in the Los Angeles Times:

"I looked at commencement and other announced graduation event speakers for 2012 and 2013 from the top 100 universities and top 50 liberal arts colleges (according to the U.S. News & World Report rankings)."

All told, he wrote, "there were only three identifiably conservative speakers at the top 50 colleges and 12 at the top 100 universities, compared with a total of 69 identifiably liberal speakers."

Like conservatives before him, Hassett concludes that liberal arts colleges are "hostile territory." One of his case studies is especially convincing. Robert Zoellick, the U.S. Trade Representative and a deputy secretary of state for President George W. Bush, who later served as president of the World Bank, withdrew from a scheduled commencement speech at his alma mater, Swarthmore College, after students objected to his association with the Bush administration. As Hassett wrote:

"If Zoellick, a moderate gentleman with an impressive record promoting women's rights as president of the World Bank, can't speak on a college campus, no Republican can."

If liberal colleges can't tolerate the likes of Zoellick, they really do have a problem. But the overall numbers may be due to another factor beyond rude liberal students plugging their ears: It keeps getting harder to find conservatives worth listening to.

In the past couple years there has been much blogosphere discussion of "epistemic closure" on the right -- the phenomenon of conservative media, politicians and intellectuals forming a closed information loop in which they more or less tell one another what they like to hear.

The resistance of liberal campuses to inviting conservative speakers confirms the phenomenon isn't purely a product of the right. Yet in Washington and on the Internet, it overwhelmingly is. (The obvious caveat: Conservatives like Ross Douthat and Ramesh Ponnuru continue to rise above the dreary mean, though it must get pretty exhausting for their small, hardy band to hold up the entire side.)

Which brings me to Jonathan Chait. Two weeks ago, he laid down the kind of gauntlet that seemed certain to generate a lively response. Chait makes a living in part by ridiculing the hypocrisies of the Republican mainstream and the lunacy of the conservative fringe. He occasionally does Democrats a similar favor (and exhibits a curious Ohio tic on the side). He is also ruthlessly analytical and highly substantive.

Chait's thesis was that the intellectual foundations of both Republican economic doctrine and the opposition to Obamacare have been obliterated by the reality of declining deficits and slowing health care costs. He wasn't kicking around Representative Michele Bachmann or Louis Gohmert or one of the other knaves of right-wing media. He explicitly went after the Republican Party's de facto policy leader, Representative Paul Ryan, and one of its leading policy intellectuals, Yuval Levin. Citing positive trends on the deficit and health care costs, Chait's attack was unsubtle:

"The Ryan worldview is that the United States is heading toward a massive debt crisis, that the crisis is driven primarily by rising health-care costs, and only his plan stands any chance of alleviating it. . . .The certainty of the imminent debt crisis, and the certainty that Obamacare would worsen rather than ameliorate it, undergirded the party’s entire strategy."

In the wake of evidence showing precisely the opposite, Chait wrote:

"The canon of Levin and Ryan has undergone no revision whatsoever. The debt crisis is 'irrefutably happening,' Ryan insisted recently. Obamacare, he said yesterday, will 'collapse under its own weight.' Ryan and his party are so certain of the foundations his worldview rests upon that he can’t even be bothered to look down at the rubble all around his feet."

Chait is one of the smartest liberals writing. His attack on conservative doctrine was direct, empirical and, to my mind, quite devastating. In the two weeks since his piece was published, no smart conservative -- Levin is the obvious choice -- has answered his challenge. It turns out Swarthmore isn't the only place missing a conservative speaker.

(Francis Wilkinson is a member of the Bloomberg View editorial board. Follow him on Twitter.)