The disappearance of the journalist Jamal Khashoggi has precipitated a new crisis in U.S.-Saudi relations. Yet that crisis has also revived a much older dilemma in American strategy: How to deal with allies that also happen to be morally abhorrent, even murderous, dictatorships.

The basic predicament has been around for over a century. As the United States established its dominance in the Western Hemisphere in the late 19th and early 20th centuries, it often cooperated with local strongmen who could provide some semblance of stability. Throughout the Cold War, containing communism required working with partners that were far from morally pure — dictators who ruled key allies such as South Korea, Turkey, Portugal and Greece at various points, as well as a clutch of Latin American and Middle Eastern despots.

The rapid spread of democracy from the 1970s through the early 2000s eased this dilemma, by aligning the frontiers of freedom more closely with the frontiers of America's European and Asia-Pacific alliances. Yet the problem has now returned, and not just in the Middle East, because of two factors.