Bernstein caps off the discussion:
Obviously, everyone has sources they trust more, sources they are somewhat suspicious of, and sources they dismiss. What Sanchez is talking about is a group of people who all agree on which sources are to be trusted -- and who have narrowed it down to a fraction of all the information out there, a fraction which is both closed and small and suspicious of any outside sources. He's actually not talking at all about ideology or issue positions; he's talking about staying in touch with reality, which as Andrew Sullivan reminds us (quoting Orwell) "needs a constant struggle."
Sanchez, Millman, and Friedersdorf are struggling. Jonah Goldberg doesn't seem to see the point of it.
Larison believes this closure isn't new:
[T]here has been an intensification in cocooning and forgetting as conservatives are now able to receive and exchange information in an almost parallel universe. In this universe, as Henninger’s column in The Wall Street Journal reminded me yet again this morning, Obama originally never intended to increase the U.S. presence in Afghanistan, when in the real world he had pledged to do this many times. When viewed from the parallel universe, Obama’s decision on Afghanistan is a surprise and a change, because it does not agree with the cartoon fantasy of Obama’s foreign policy that movement conservatives and their allies have constructed for themselves. This happens all the time, and not only are these mistakes never corrected, but the people who make them on a regular basis enjoy great success within the confines of the movement. This is not a “closing” of something that was once open, but the normal operation of an ideological movement.