JOHN Patrick Diggins doesn’t fit neatly into the usual cat- egories.  He is pungently impatient with successive waves of academic radicalism—“Frankfurt School Marxism,” “postmodernism,” “civic republicanism,” “multiculturalism,” and “neopragmatism,” among others. He favors a patriotic, though not uncritical, nationalism and insists that Western civilization is the source of what matters most about America. All this has led many to believe that Diggins is some kind of conservative.  But he isn’t. He is scathingly critical of contemporary conservatives for what he sees as their misplaced nostalgia, near-total misunderstanding of American history, and Reaganite triumphalism.