The real interests at stake in Syria include stopping a humanitarian nightmare that has claimed more than 100,000 lives; frustrating the designs of Iran and its partners; reinforcing the norm that chemical weapons cannot be used with impunity; and demonstrating that what the US says is to be taken to the bank by friend and foe alike.
But any assessment of interests must include both the likely costs and consequences of acting and competing interests. In the case of Syria, what it would take to oust the Assad regime would be considerable given its determination and external sources of support. Just as important, the costs would mount exponentially if the goal was to bring about a successor Syrian government committed to peace in the region and tolerance at home. This could require prolonged presence of outside forces, and even then (as both Iraq and Afghanistan have shown) there is no certainty that order would materialise.
US officials also need to keep in mind that Syria is hardly the whole of American national security. Dealing with Iran's nuclear ambitions – in the first instance diplomatically, possibly militarily if negotiations fail – will require great attention. The US also needs to free-up resources to help maintain stability in the Asia-Pacific, where many of the major powers of this era interact amid growing nationalism and without much in the way of diplomatic arrangements. And no less important is tending to the fraying domestic foundations of American power, from infrastructure and schools to unfunded entitlement obligations.
So what would a policy look like that balanced a need to act meaningfully with a need to show restraint?
First, the US would strike the Assad regime in response to its repeated use of chemical weapons. Such an air strike in Syria would have to be more than token; it would have to inflict real cost and pain if it were to achieve the objective of discouraging the use of weapons of mass destruction by Damascus or anyone else.
At the same time, the military action could not be open-ended or require a significant military commitment. (This should help in the effort to win over Congress.) Using cruise missiles as some have suggested to destroy airfields would be one option.
Implicit in all of the above is that direct military action would be part of US policy but not the bulk of it. The administration has talked about providing significant arms to those elements of the opposition it supports. Yes, some of the weapons will end up in the wrong hands, but arming the more moderate opposition needs to happen as it offers the best way over time to affect the military balance and the future of Syria at an affordable cost.
Third, the US should continue to shore up Syria's neighbours and especially Jordan that is absorbing so many of the refugees. Conversations with neighbours should also involve contingency planning for possible moves by Syria or its partners to widen the war.
Last, one can consider diplomacy, but the reality is that the timing is premature. Russia is not willing to back away from the regime, and there exists little interest within Syria to compromise. This will only change when the situation on the ground changes, something that will only happen with effort and time.
In short, the US needs a strategy that it is prepared to implement and live with. Such an approach will not oust the regime or end the war any time soon, but it does provide a trajectory that protects some of its immediate interests and can be squared with larger American national security concerns both abroad and at home.
The author is president of the Council on Foreign Relations. His most recent book is 'Foreign Policy Begins at Home.'