With the U.S. and NATO's thumb firmly on the scale, the balance of power in Libya seems to be shifting steadily toward the rebel forces. That's bad news for the Qaddafi family, though their lack of attractive alternatives to fighting on makes it unlikely that they will simply surrender. This outcome is also not that surprising, as the Libyan military was never a first-class fighting force and it was not going to have real trouble standing up to the rebel forces once they started getting lots of outside help. The danger, however, is that the rebel forces will not be able to consolidate control over the entire country without a lot more fighting, including the sort of nasty urban warfare that can get lots of civilians killed.
As with the invasion of Iraq, in short, the issue wasn't whether the West could eventually accomplish "regime change" if it tried. Rather, the key questions revolved around whether it was in our overall interest to do so and whether the benefits would be worth the costs. In the Iraqi case, it is obvious to anyone who isn't a diehard neocon or committed Bush loyalist that the (dubious) benefits of that invasion weren't worth the enormous price tag. There were no WMD and no links between Saddam and al Qaeda, and the war has cost over a trillion dollars (possibly a lot more). Tens of thousands of people died (including some 4500 Americans), and millions of refugees had to flee their homes. And for what? Mostly, a significant improvement in Iran's influence and strategic position.
In the Libyan case, same basic question. Hardly anyone thinks the Qaddafi family deserves to run Libya, and few if any will mourn their departure. But assuming the rebels win, will the benefits of regime change be worth the costs? Secretary of Defense Gates has reported that the war has cost the United States about $750 million thus far, which is not a huge sum by DoD standards but not exactly trivial in an era of budget stringency. More troubling is the cost to Libya itself: NATO and the US intervened to ward off an anticipated "humanitarian disaster" (which might or might not have occurred and whose magnitude is anyone's guess); what we got instead was a nasty little civil war in which thousands may already have died (and the fighting isn't over yet). So we can look forward to lively debate on the wisdom of this intervention, with advocates claiming that we prevented a larger bloodbath and skeptics arguing that there was never any risk of a genocide or even a deliberate mass killing and that our decision to intervene actually made things worse.
Meanwhile, the Obama administration is about to hit the 60 day deadline imposed by the War Powers Act, and so it is marshaling a lot of clever lawyers to find some way to keep the war going. But here's a radical suggestion: why not just go to Congress and ask for authorization? Such a step would be consistent with the U.S. Constitution, and President Obama made this very point himself before he became President. As he told the Boston Globe in 2007: "the president does not have power under the Constitution to unilaterally authorize a military attack in a situation that does not involve stopping an actual or imminent threat to the nation." And if the case for this war is so strong and it is so clearly in our vital interests to do it, surely the articulate advocates in the Obama Administration won't have any trouble convincing Congress to go along.
At the same time, the US and NATO had better be thinking long and hard about what they are going to do if and when Qaddafi falls. As we are now seeing in some other contexts (e.g., Egypt), revolutionary change is usually chaotic, unpredictable, and violent, and it creates opportunities for various forms of mischief. These dangers loom especially large in Libya, due in good part to the lack of effective political institutions and the likelihood that some of the people we are backing now will want to settle scores with loyalists. And that possibility means there's also a risk of the same sort of loyalist insurgency that sprang up in Iraq, possibly rooted in long-standing tribal divisions.
So if the liberal interventionists who got us into this war want to make their decisions look good in retrospect, they had better have a plan to ensure that political transition in Libya goes a lot more smoothly than it did in Iraq. And you know what that means, don't you? We'll be there for longer than you think, and at a higher cost than one might hope. But no worries; it's not as though we have any other problems to think about (or spend money on) these days.