For more than a decade the air has been filled with assertions that American conservatism is in terminal disarray—exhausted, fractured, and no longer capable of governing. The spectacular populist insurgency of 2015–16 appears to many observers to mark the demise of an intellectual and political establishment that has outlived its time.

Is this true? Before we can properly assess conservatism’s present predicament, we first need to understand how the present came to be. I propose to do this through the lens of the intellectual history of American conservatism after the Second World War, when the conservative community as we know it took form.

Perhaps the most important fact to assimilate about modern American conservatism is that it is not, and has never been, monolithic. It is a coalition—a coalition built on ideas—with...