To conservatives, this talk of communism's root causes looked like an effort to rationalize evil, to suggest America's real foe was not communism itself, but the forces that produced it. "The fact that some poor, illiterate people have 'gone Communist' does not prove that poverty caused them to do so," insisted Barry Goldwater, the first National Review-style conservative to win a Republican presidential nomination.

On domestic policy, the argument was similar. For liberals, the New Deal had tempered capitalism's instability and inequality, thus preserving Americans' belief in democracy when people were losing it around the world. America's ongoing task, Niebuhr argued, was to "make our political and economic life more worthy of our faith and therefore more impregnable." But for conservatives, the liberal push for equality at home did not strengthen America in its cold-war struggle; it undermined the very ideological clarity upon which that struggle relied. Viewed from the right, Franklin Roosevelt had already moved America perilously far along what the Austrian émigré economist Friedrich von Hayek famously called the "road to serfdom." And the more the United States aped communism, the less it would recognize its evil. "The liberal's arm cannot strike with consistent firmness against communism," Burnham wrote, "because the liberal dimly feels that in doing so he would be somehow wounding himself."

In the years since 9/11 restored foreign policy to the heart of American politics, these cold-war debates have returned in another form, with the critical difference that only one side knows its lines. Even before the attacks, many conservatives feared America was emasculating itself yet again. In a one-superpower world, they argued, America no longer had to tailor its foreign policy to the wishes of others. And yet, in the conservative view, the Clinton administration had permitted constraints on American power, playing Gulliver to foreign Lilliputians intent on binding it in a web of international institutions and international law. Predictably, conservatives attributed this submission to America's lack of faith in itself. The "religion of nonjudgmentalism," wrote William Bennett in the book "Why We Fight: Moral Clarity and the War on Terrorism," "has permeated our culture, encouraging a paralysis of the moral faculty."

In his first eight months in office, President Bush aggressively reasserted American freedom of action, repudiating no fewer than six international agreements or institutions. And after 9/11, he began depicting this freedom to act alone as a means not merely of safeguarding American interests but also of liberating American virtue so it could remake the world. In 2002, the conservative columnist Charles Krauthammer noted that "people are now coming out of the closet on the word 'empire.' " And that discussion had an idealistic cast. For its proponents, "empire" was usually preceded by the adjective "benign" or "liberal." In other words, the United States would rid itself of external impediments but nonetheless act in the global good, uncorrupted by the temptations of unrestrained power.

It has not turned out that way. On global warming, an America liberated from international restraint has acted irresponsibly; in our antiterrorist prisons, we have acted inhumanely. And from the moment the United States invaded Iraq, the Bush administration's complacent certainty of its own benevolence has blinded it to the dangers of colonial rule. While the authors of the Marshall Plan avoided remaking Europe's economy, for fear of sparking nationalist resentment, the head of the Coalition Provisional Authority, L. Paul Bremer III, unilaterally rescinded Iraq's import tariffs on foreign goods. Bremer may have thought he was acting on Iraq's behalf, even without its people's consent. But that is only because he lacked the self-consciousness and humility to see that he was not. As Larry Diamond, a more reflective C.P.A. official, noted: "American political leaders need to take a cold shower of humility: we do not always know what is best for other people, even when we think it is their interests we have in mind. And as I saw during my time in Iraq, it was frequently our interests that were driving decisions we were trying to impose." Niebuhr couldn't have said it better himself.

But for all their practical failures, conservatives have at least told a coherent political story, with deep historical roots, about what keeps America safe and what makes it great. Liberals, by contrast, have offered adjectives drawn from focus groups and policy proposals linked by no larger theme. In his 2004 convention acceptance speech, John Kerry used variations of the word "strong" 17 times. For the 2006 campaign, Congressional Democrats have unveiled a national-security vision they call "tough and smart." It calls for more spending on homeland security, energy independence and Special Forces. But these disparate, worthy proposals are not grounded in an account of the world America faces, or the sources of American strength.

In fact, present conditions make liberalism's forgotten story especially compelling. The unprecedented post-cold-war gap between America's military power and every other nation's does not make international institutions unnecessary, as the right argues; it makes them even more essential. The liberals of the early cold war, who had seen depression and war cross the oceans and imperil the United States, believed America could guarantee neither its prosperity nor its security alone. And globalization makes that even truer today. The world's increased integration has left the United States more vulnerable to pathologies bred in other nations. So more than ever before, American security requires economic, political and even military interventions in the internal affairs of other nations: to stop bird flu from spreading in rural China, corruption from sparking a banking collapse in Thailand or jihadists from plotting in Pakistan.