It hasn't worked. Classic counterterrorism tactics have done a very effective job of wiping out Taliban leaders, but the Taliban keep regenerating thanks to the Afghan government's scant legitimacy. Endless American efforts to get Afghan President Hamid Karzai to behave other than the way he is inclined to behave have come to nothing. But does that necessarily mean that Biden was right? His argument was always, "It's Pakistan, stupid." The experience of the last few years, however, has shown both that the United States has far less leverage over Pakistan's military leaders than it thought, and that Pakistan's pathologies are even deeper than we understood. Is there any graver example in the world of "We must, but we can't"?

And so there is much to feel chastened about. Last year Peter Beinart, a former New Republic editor and a liberal supporter of the Iraq war, repented with a vengeance by writing The Icarus Syndrome: A History of American Hubris. Beinart came down so hard on poor Woodrow Wilson, and on Wilsonian idealism in foreign affairs, that the Council on Foreign Relations' Leslie Gelb, an arch-realist, took him to task in the New York Times Book Review. Idealism is not, or rather need not be, a species of hubris; it was, after all, Wilson's explicit and eloquent appeal to national ideals that persuaded a very reluctant American public to enter World War I.

There is a very real danger that our reaction to the discovery that we can't do everything will be to conclude that we can't do anything. We should rein in our hubris, tend to our own garden, patrol our own borders (and Persian Gulf sea lanes too, of course). We should not, in John Quincy Adams's now-much-quoted phrase, go abroad in search of monsters to destroy. But as we learned on 9/11, the world beyond our borders can do terrible harm to us, as it could not in 1821. And it can, lest we forget, bring great benefit as well.

We have been given a second chance to get things right. Just as the last decade began with the terrorist attacks, this one has begun with the Arab Spring. It is, in effect, 2002 once more: We stand at the very beginning of a new moment in history, its outcome very much unknown. And, of course, what is centrally different about this moment is that the peoples of the Arab world have acted on their own. The irrelevance of outsiders has made it impossible for Arab autocrats to discredit the democratic movement, as they were able to do in the face of Bush's blustering about freedom, and as the Iranian government sought to do in 2009. And yet we have just seen overwhelming proof that outsiders can decisively tip the scales on behalf of Arab peoples.

I am thinking, of course, of Libya. The NATO bombing campaign dislodged Muammar al-Qaddafi's regime without undermining the rebels' own legitimacy. Conservatives now belabor Obama for "leading from behind," or letting France -- France! -- take the lead; but Obama understands that the Arab Spring is not some sort of test of American power or primacy. American capacities were indispensable to the NATO effort, but no one can say that America delivered Tripoli to the rebels. That's not a bad model for the future.

It is, of course, no secret that American firepower can work wonders. But now the hard part begins. In Libya, as in Egypt and Tunisia, the tyrant is gone, and the burden of creating a future different from the past has fallen on people with no experience of self-government. This is where democracy promotion becomes very real, but also very unglamorous. Libya doesn't need money -- save for its own unfrozen assets -- but it will need a lot of diplomatic hand-holding and help with the establishment of political parties, electoral commissions, a parliament, and so on.

OK, maybe that's not so hard. Here are some hard questions: What are we going to do in Egypt if the Muslim Brotherhood captures a plurality of seats in elections this fall? Are we going to say that democracies disqualify themselves when people freely choose Islamists? And what about Bahrain, where Obama was bold enough to publicly demand reform -- and where the regime has carried out a Potemkin version of dialogue with the opposition? Is Obama prepared to threaten serious consequences, or will he back down in the name of preserving alliances, as Bush did in Egypt in 2005?

Obama has often expressed his admiration for Niebuhr and the realists. He will err on the side of restraint. Perhaps, with all we've been through, that's a good thing.

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