Judge Richard Posner has been one of nation's most renowned conservative legal thinkers since President Ronald Reagan appointed him to the 7th U.S. Court of Appeals in 1981. But, in a candid interview with NPR on Friday, Posner was unafraid to step away from partisan talking points to voice his irritation with today's Republican Party, even saying a real deterioration in conservative thinking has divided him from a base which he described as a crowd of lunatics.

I've become less conservative since the Republican Party started becoming goofy, Posner said, adding that the party has become increasingly bullish over the past decade.

Posner hasn't become a liberal acivist, it should be noted. He still voiced his admiration for Republican icons such as Reagan and economist Milton Friedman. Reagan, unlike many prominent conservatives today, had good ideas and instincts, Posner said, although he admitted the former president was not on the same intellectual level as Friedman.

The latest bit of goofiness to attract Posner's scorn is the political attacks on Chief Justice John Roberts, following his decision to uphold the Obama administration's health care reform law.  Republicans, who previously sang praises for Roberts -- appointed to the U.S. Supreme Court by President George W. Bush -- were blindsided by his decision, leading to a barrage of criticism in an attempt to discredit the opinion upholding the law.

Posner said the Republicans attacking Roberts are making a very serious mistake, even suggesting it could push the Chief Justice away if he decides he has no home on the right.

I mean, what would you do if you were Roberts? All of a sudden, you find out that the people you thought were your friends have turned against you, they despise you, they mistreat you, they leak to the press. What do you do? Do you become more conservative? Or do you say, 'What am I doing with this crowd of lunatics?' Right? Maybe you have to reexamine your position, Posner said.

Posner also recently called out conservative Justice Antonin Scalia, in a column published on Slate. Reflecting on Scalia's combative dissent in the recent Arizona immigration case, in which he specifically attacked President Barack Obama's immigration policies, Posner wrote that it wouldn't surprise [him] if Justice Scalia's opinion were quoted in campaign ads.

Posner, who is also a senior lecturer at the University of Chicago Law School, has authored dozens of books on law and economics. In 2000, the Journal of Legal Studies identified him as the most-cited legal scholar of the 20th century.