Mr. Boot is a senior fellow in national security studies at the Council on Foreign Relations.

After hardly mentioning Libya for months, President Obama and his aides are now taking an understandable victory lap. With Tripoli having fallen to rebel forces on Aug. 21, after six months of war, the president's supporters are even suggesting that Operation Unified Protector, as the international intervention was formally known, offers a new model for the use of force: one where the U.S. acts at low cost to defend human rights by putting allies into the lead. An anonymous administration official dubbed this "leading from behind"—a term that has raised hackles on the right but that, some argue, has been vindicated in Libya.

In truth, it's too soon to tell. Recall how glorious the future looked in Afghanistan in December 2001. The Taliban had been toppled in two months, and the U.S. had brought about their downfall with a few hundred CIA officers and Special Operations Forces backed up by air power. This brought giddy predictions—which ignored the crucial role of the Northern Alliance—that precision munitions and a few eyes on the ground could work miracles.

Then reality set in, as we discovered—not for the first or last time—that it is much easier to topple a regime than to replace it. Smart bombs can destroy a dictator's army but they cannot build a democracy or even suppress an insurgency. That requires boots on the ground. We did not have enough in either Iraq or Afghanistan, and neither did our allies. 

Now in Libya it appears there will be no foreign boots on the ground—no peacekeeping force from NATO, the United Nations or any other organization. The Transitional National Council will be left on its own to deal with the difficult task of ending the last-gasp resistance of Moammar Gadhafi's henchmen, securing government arsenals (which include chemical weapons and portable anti-aircraft missiles), and trying to establish rule of law.

The rebels have shown a fairly impressive ability to govern Benghazi, but running the entire country is a more difficult task. Whether they can carry it off successfully will determine history's judgment on Operation Unified Protector—and on America's role in Libya... ..