Robert J. Samuelson has an interesting, and rather pessimistic, piece on "the future of think tanks". Samuelson deals specifically with the Heritage Foundation, particularly because Stuart Butler, for 35 years a senior researcher at Heritage and "among the most visible figures -- possibly the most visible -- shaping conservative views on social policy", is moving to the Brookings Institution.
Samuelson thinks that this move is justified by the "mutation" of Heritage and, similarly, of many other Washington think tanks, with a few exceptions (including Brookings):
Most think tanks were once idea factories. They sponsored research from which policy proposals might flow. In the supply chain of political influence, their studies became the grist for politicians' programs. But think-tank scholars didn't lobby or campaign. Politicians and party groups did that. There was an unspoken, if murky, division of labor. This was Butler's world.
But it's disappearing, and many think tanks -- liberal and conservative -- have become more active politically.
I have posted before on the subject, here, and a rather interesting discussion developed in the comments.