Every republic, large and small, lives with a tension between the need for public-spirited, civic-minded leaders and the inevitable pull of private interests and affections. The larger and wealthier the republic, the greater the challenge, because the republic’s officials must live and move and work in an atmosphere of commercial wealth and foreign lucre — which creates not only direct temptation but also, more subtly, a fear that you are failing your family, your children, if you remain unbought.

The Roman republic in its waning years managed this tension by creating a zone of self-enrichment that was outside the res publica. The public-spirited Roman served the republic in the city of Rome and then got rich somewhere else, far away and out of sight. You climbed the cursus honorum, you reached the office of praetor or consul, you governed honorably and ably (at least in theory), and then your reward was to become a provincial governor and have the chance to squeeze the inhabitants of Hispania Ulterior or Gallia Narbonensis for every last denarius — subject only to occasional prosecution for “abuses” if you made the wrong enemies back home.

The American republic, more idealistic and less brutal than its Roman antecedent, doesn’t send former cabinet officials and senators off to practice extractive taxation everywhere that we have military bases. Instead, we’ve developed a more complicated interplay between public service and private enrichment, a labyrinthine system of consultancies and adviserships and directorates and boards in which the dedicated public servant can make enough money to keep up with the cost of tuition at Sidwell or Exeter without ever taking anything so embarrassing as a bribe.

The ideological grease in this system is the belief that the American businessman, the American soldier and the American diplomat are all fundamentally doing the same work, expanding the Pax Americana one newly opened market, one toppled strongman and one baby democracy at a time. So why shouldn’t our public servants move back and forth between these realms — selling arms to our allies one day, serving on a do-gooding foundation funded by allies and defense contractors the next, helping those allies lobby our government the day after that? After all, all these projects serve the same goal: A world of capitalist democracies at peace with one another, free to get rich under the umbrella of the American military.