Will a blow on Syria be a blow for justice?

The American debate over a military strike on Syrian forces is shifting from “whether” to do it to “how” to do it. In other words, Congress may yet decide a strike is right and just. Equally hard is making sure the conduct of the US military is also just.

In “just war” theory, the means of war must be in proportion to the actual threat and to the political ends. A strike on the Syrian military, for example, would not be just if a mistargeted cruise missile harms as many civilians as were killed last month in a poison gas attack. Nor should the use of force go beyond the goal of deterring further use of chemical weapons. A strike also should not broaden violence in unexpected ways, such as drawing in Iran or Israel.

Lawmakers are struggling with these issues of “just” means as they prepare to vote on a resolution that would both support a strike and set limits on the timing and extent of operations. Congress is right to try to make the unknowns as known as possible. As Joint Chiefs Chairman Gen. Martin Dempsey warns, “We could inadvertently empower extremists or unleash the very chemical weapons we seek to control.”

The task for Congress has not been easy. President Obama at first promised a “limited and proportional” attack. Yet later he spoke of a “broader strategy” to strengthen the Syrian opposition and bring peace to the region. Such an escalation of goals does not help Congress reach a consensus on means.

In his 2011 military intervention in Libya, Mr. Obama did not seek approval from Congress, and later changed that campaign’s goal from protecting endangered civilians to one of regime change. The airstrikes were sent on new missions. Congress took note and now rightly questions Obama’s intentions as commander in chief in a Syrian campaign.

Not only Libya serves as a lesson. “After the fiasco of Iraq and over a decade of war, how can this administration make a guarantee that our military actions will be limited?” asked Sen. Tom Udall (D) of New Mexico. Other lawmakers question Obama in his claim that his dramatic increase in the use of drones against Al Qaeda is both proportional to the threat and a just use of violence for the purpose of self-defense.

Some lawmakers want to limit any operation in Syria to 60 days. Others seek to prevent a second wave of strikes unless President Bashar al-Assad orders another gas attack. A few hawkish lawmakers say the only way to uphold the international ban on the use of chemical weapons is for the United States to end Syria’s civil war with American boots on the ground. (Secretary of State John Kerry told Congress he wants to retain the option of using combat troops.)

Lawmakers must try as best they can to sort out the moral dimensions of how to wage this war – even before it starts. They are dealing with probabilities of its success as well as the principle of proportionality in how the war is conducted. Even if they affirm America’s role as a military superpower in striking Syria from afar, they must do so as a moral superpower.