Vladimir Putin has threatened to use nuclear weapons in Ukraine. We need to be prepared to respond to Putin's threats—and to do so effectively we have to understand the role of nuclear weapons in Russian strategy, in American foreign policy, and in the current global order. To consider these questions, we are joined by Harvard professor of government Stephen Rosen. Drawing on his profound knowledge of the Cold War, Rosen explains the role nuclear weapons have played since the Soviet era. Then as now, Russia’s threat to deploy nuclear weapons aims to deter its adversaries from intervening to defend an ally. Though we must be judicious in our actions, Rosen explains why the West cannot afford to give in to nuclear blackmail. Beyond the potentially disastrous consequences for Ukraine, he contends that surrendering to Putin’s threats would embolden other nuclear states to pursue wars of conquest. Rosen also outlines approaches we should consider to counter Putin’s other potential escalations.