One of the fondest expressions around is that [America] can't be the world's policeman. But guess who gets called when suddenly someone needs a cop.

Powell is critiquing a common strain of U.S. foreign-policy rhetoric—"we can’t be the world’s policeman"—by pointing to the recurring reality that, in crises, other states and international institutions often look to the United States for decisive security action. The “cop” metaphor frames American power as both burdensome and expected: the U.S. may resist the role, but its unique military reach and political influence make it the default responder when order breaks down. The line also implies a warning about responsibility and consequences: if the U.S. is repeatedly summoned, it must weigh when intervention is justified, how legitimacy is secured (allies, UN mandates), and what long-term commitments follow from acting as the enforcer.