But a more principled reason than “you do it too” is that American intelligence collection is a crucial part of America’s broader security posture, and that security posture has underwritten not only our own but also our allies’ security for almost seven decades now. We don’t just collect intelligence so that we can secure ourselves; we collect intelligence so that we can secure the many countries we’re committed to defending. And doing that effectively means more than just collecting intelligence on our potential enemies. Bear in mind that many of our allies have feared not only the Soviet Union or Iran or North Korea—but have also feared each other. Thus a crucial part of U.S. security policy since 1945 has been managing and reducing tensions among our allies, including allies with bitter memories and clashing interests. Once again, take the case of Germany and remember that NATO’s first Secretary General summarized common European thinking in describing NATO’s basic purpose: to “keep the Americans in, the Russians out, and the Germans down.”

Nor is this merely an historical problem—observe the deep tensions today between U.S. allies South Korea and Japan or between Israel and the Gulf nations. And just as overweening American military power has over time reassured many of our allies that they could rely on the United States to insure them against the possibility of resurgent German, Japanese or Turkish military power, so too do formidable U.S. intelligence collection capabilities contribute to that reassurance. Nor do the Germanys and Japans of our alliance structure suffer from this. Quite the contrary, they have no better way of persuading their neighbors of their good faith than American oversight.

It is crucial to maintain our ability to spy on allies, but misguided excessive pressure from our allies might well persuade us to make a bad decision to constrain or even suspend this ability. We should therefore not be shy about making these points, both here and in the international arena. Of course, these arguments presume some degree of trustworthiness and even benevolence on the part of the United States. But is such presumption unreasonable? Has the United States used its military and intelligence power for or against the interests of its allies? Have they benefited or suffered from it? Certainly we should not be given carte blanche—as Americans, we are believers in checks and balances. But these points do suggest that our allies should think very carefully before pressing the United States too far on this matter.

Ultimately, though, Americans should decide for themselves whether their government should be prepared to spy on allies. One option would be to return to the policy of “gentlemen don’t read each other’s mail” that we (at least partially) adhered to in the 1930s, a decade not distinguished by the wisdom of its foreign policies. But while a public prohibition on spying on our allies would certainly represent a noisy gesture of our idealism, it would not represent a judicious one. The other option would be to retain our ability to collect intelligence on or about our allies, but to redouble our intention to do so only for sound and defensible reasons. The latter course, while perhaps a somewhat deflating admission of the enduring imperfection of life in the international arena, represents the prudent course.

Elbridge Colby served with the Office of the Director of National Intelligence and with the President’s Commission on the Intelligence Capabilities of the United States Regarding Weapons of Mass Destruction.

Image: Flickr/Kate Ter Haar. CC BY 2.0.