He classifies political affinities along a 6-spoke wheel: progressives, pragmatic libertarians, dogmatic libertarians, conservatives, corrupt Republicans, corrupt Democrats.
He writes,

I would like to argue that most of the really important public policy issues are not even part of the ongoing debate in the press.

He proceeds to list six policy failures: occupational licensing, the drug war, taxation of capital rather than consumption, zoning restrictions, and the tax deductions for mortgages and health insurance.

From a pragmatic libertarian perspective (which I presume he is coming from), these are important issues. But Sumner’s point is that the real-world politicians (the corrupt Democrats and the corrupt Republicans in his framework) line up together against this pragmatic libertarian view. Since the real-world politicians do not disagree with one another, there is nothing for the media to report.

By the way, “corrupt” is shorthand for “pandering to interest groups.”