In the 1960s and ‘70s, it was fairly common for leftists to describe the U.S. as not just misguided or flawed, but sick. On Sunday, Daily Kos’s Mark Sumner trotted out that metaphor when he asserted that President Reagan “introduced [an] infection” to this country, one which caused Americans to believe that “to save our nation, we have to treat our government like a threat.” Since the Reagan years, Sumner claimed, “conservatism has been more than just an argument about tax rates and regulat[ions]. It's become an open and honest war on the whole idea of governing. By opening a...