If the country becomes a failed state, the biggest winner will be al Qaeda. Our allies will be the losers.
In response to recent reports that the Assad regime in Syria may have used chemical weapons against the rebel opposition, President Obama declared that such a development, if confirmed, would be a "game changer."
But regardless of the kind of weapons Assad is using to slaughter his people, Syria is already a moral and strategic calamity that is growing worse by the day, not only for Syrians and their neighbors but also for vital national interests of the United States. That is why it is already past time for a change in American policy toward Syria.
With over 70,000 dead, more than a million refugees and no end in sight, it may seem difficult to imagine how the situation in Syria could get any worse—but it can and will, if the current course is allowed to continue.
Assad's killing machine is tearing Syria to pieces, miring the country deeper and deeper in a sectarian civil war that could rage for years. The biggest winner if Syria becomes a failed state is likely to be al Qaeda, which is already making inroads by exploiting the anger of Syrians at the West for our refusal to provide them with the help they need.
In addition to giving Islamist extremists a new foothold in the heart of the Middle East, a radicalized and balkanized Syria is also certain to spill over, threatening the stability and security of other states in the region, including U.S. allies in Jordan, Turkey, Iraq, Lebanon and Israel.
This is very much like the nightmare scenario the U.S. confronted in Iraq in 2006—a catastrophe that was only narrowly averted because of the troop surge. As in Iraq, it is not too late for the U.S. to change course to salvage its Syria policy, but time is running out.
Unfortunately, actions that might have been decisive if undertaken earlier are now likely to be inadequate. Providing weapons directly to the Syrian opposition is still absolutely necessary, but it is no longer likely to be sufficient, by itself, to change Assad's calculations or to alter the trajectory of the conflict.
Such an effort to arm the opposition—particularly if it is attempted in secret—will also do nothing to address the fury of ordinary Syrians toward the U.S., whom they understandably see as callously indifferent to their suffering.
What is required now is a limited campaign of U.S.-led airstrikes to neutralize Assad's planes, helicopters and ballistic missiles, which are being used to terrorize the Syrian population. Taking such a step would not require the U.S. to act unilaterally, nor would it involve any American boots on the ground.
At the very least, U.S. Patriot missile-defense batteries that are already deployed near the Turkish-Syrian border could be used to stop the barrages of Assad's Scud missiles that have been raining down indiscriminately on the towns and cities of northern Syria.
There is no more stark illustration of our refusal to help Syrians, despite having the military means to do so, than the continuing devastation caused by the Syrian regime's ballistic missiles mere miles away from our Patriot batteries.
Conversely, if the Patriots were used to establish a safe zone in northern Syria, they would instantly become a powerful symbol of U.S. solidarity with Syrians, bolstering moderates in the opposition and giving them the space they need to organize inside the country.
America and its allies also need to start genuine planning for the day after Assad goes.
As in the Balkans in the 1990s, peacekeeping forces will be needed if there is any prospect of holding Syria together, along with a large-scale international effort to train Syrian forces that can maintain security. If we wait until after Assad falls to begin this discussion, it will be too late.
It is often said that the longer the conflict in Syria grinds on, the worse the situation on the ground grows. That is true. But it is equally true that the longer the U.S. refuses to lead, the higher the cost will be when America ultimately decides it must get involved because of the country's vital national interests at stake in Syria.
Rather than waiting for proof that Assad has used his chemical weapons, the United States should introduce its own game-changer to the conflict: strong, decisive leadership.
*A version of this article appeared April 3, 2013, on page A17 in the U.S. edition of The Wall Street Journal.**Mr. Lieberman is a former four-term U.S. senator from Connecticut.