Joseph Nye has said security is like oxygen: everyone enjoys it when it is present and few fully appreciate it until it is absent, at which point regaining it becomes an all-consuming obsession.

At a recent workshop on grand strategy, one of my colleagues observed that American power may be like gravity: it is hard to evaluate its reach and impact until it is gone, at which point we are likely to miss it acutely.

He is on to something that policymakers have recognized but have struggled to articulate in a way that won’t get mocked by academics (cf. “indispensable power”).  Certainly the United States has not always wielded its power perfectly, and there are doubtless instances when some (perhaps many) other international actors would have preferred “less United States involvement.” But the United States has been a critical provider of global public goods, especially global public goods in the security sphere and a world where the United States is both unwilling and incapable of providing those public goods is likely to be a world far less congenial for many global actors — including, ironically, many who have made a cottage industry of blaming America first for the world’s problems.

Perhaps the question is best put this way: what global problem will be easier to solve if the United States is weaker relative to other countries and, feeling that weakness, is less-willing to engage globally?