Now that the end of the Assad regime in Syria is a foregone conclusion, the Obama administration is facing the possibility of a nightmare scenario that makes last year’s unwinding of Libya look easy to manage by comparison. Syria is both more explosive and more complicated, less likely to hold together when the government collapses and far more dangerous to the region because of its location at the heart of the Middle East.

Until now, the White House has had the luxury of playing for time. Get the election over with, went the thinking, and then we’ll deal with it. In the last few days, however, the rebels have gained greater momentum and Assad and his supporters are on the defensive. It’s late in the game. The government has lost control of the borders and its forces have withdrawn from important parts of the country. The noose is tightening on Damascus itself.

The downfall will be messy, but the United States and its allies have options that can limit the collateral damage and lay the groundwork for a future that would give Syria’s people reason to hope for something better than what they had under Assad.

The first step is to have in place a unified opposition that can provide transitional leadership until Syrians are able to decide for themselves what they want by way of a democratic election.

The only bright spot so far is that U.S. and European leaders have managed to forge such a group, the Syrian Opposition Council, which won recognition on Wednesday from 100 countries, further isolating the Assad regime.

It may be too late for the group to broker a political settlement, given all the blood that’s been spilled — at least 40,000 dead — and Assad’s intransigence. But the existence of this civilian body is indispensable. Whether it can hold together for long is open to question, but it serves both as a needed counterweight to the anti-Assad forces with weapons and as a vehicle to dispense U.S. and European aid and resources within the country and thus gain legitimacy in the eyes of Syrians.

Another critical move is to isolate and diminish the influence of Islamist extremists who have played an important role in the struggle to topple the government. The administration took an important step in this direction this week by labeling the so-called Nusra Front a branch of al-Qaida in Iraq, a terrorist group.

The risk of alienating an important segment of the rebels must be balanced against the greater need to ensure that nationalist, democratic forces emerge victorious in a post-Assad Syria.

Like it or not, the United States must get more involved in the nuts-and-bolts of the military endgame, even supplying weapons if necessary. The task has been outsourced to allies like Saudi Arabia because of U.S. fears that weapons would fall into the wrong hands.

But now that a political solution seems practically impossible, a hands-off approach runs the risk of having the United States seen as unserious. It would be less likely to influence the military forces that will have a say in running Syria in the future.

Supplying weapons to mainstream forces and secular rebels also gives these forces equal weight with the jihadist fighters armed by others.

The last thing the United States should do in Syria is put boots on the ground. That’s why the Obama administration must get more deeply involved to influence the outcome and avoid a victory by extremist factions. There are pitfalls on all sides, but it’s time to stop standing on the sidelines.