The last twenty years? AEI was founded in 1943, Heritage in 1973, Cato in 1977, and the Hoover Institution was originally established in 1919, although it did not come into its present form until 1957. Does this man have problems with arithmetic?(Weren't we just talking about the exclusion of arithmetic?)
Academic leftists who have trouble with the idea that some people might take issue with them of their own accord are nothing new. Years ago, some students decided to stop griping about the dominant leftist culture at the University of Wisconsin and established the Badger Herald. (Some of the founders of the Dartmouth Review, which claims to be the pioneer conservative voice on a lefty campus may have been in diapers in 1969.) From time to time the university-funded Daily Cardinal (cardinals are red, so were the editors' diapers) would claim that without funding from National Review or some such place there would be no Badger Herald. We might have a better debate if advocates -- from whatever position -- would engage the ideas rather than attempt to identify the hidden powers behind the disseminators of the ideas.
And again, I have to wonder about the power of the hidden powers. The Shriners had to sell Medinah Temple. Apparently the Vast Right Wing Conspiracy was not able to compel the Badger Herald to toe the party line: it is a sufficiently mainstream campus paper these days that something called the Mendota Beacon has emerged at the Herald's right in Madison.
(Disclosure: I did some reporting and editing for the Badger Herald in 1971-1972.)