If Russia does want to limit its involvement in Syria, the threat of limited strikes should persuade it to make the Syrian leader behave.
The Obama administration wants to reduce the violence and suffering in Syria and, at the same time, quash jihadist groups there. This is why the White House is now pushing a plan for the United States to cooperate with the Russian military in Syria, sharing intelligence and coordinating airstrikes against the Islamic State and the Qaeda-affiliated Nusra Front. In return, Russia would force the government of Syria's president, Bashar al-Assad, to stop using barrel bombs and air attacks in areas in which neither extremist group is present.
Wiping out terrorist groups in Syria is an important goal and, after years of death and destruction, any agreement among the country's warring parties or their patrons may seem welcome. But the Obama administration's plan, opposed by many within the CIA, the State Department and the Pentagon, is flawed. Not only would it cement the Assad government's siege of the opposition-held city of Aleppo, it would push terrorist groups and refugees into neighboring Turkey. Instead, the United States must use this opportunity to take a harder line against Mr. Assad and his allies.
Secretary of State John Kerry hopes that this understanding with Russia will help lead to progress on other issues, including restoring the "cessation of hostilities," a partial truce that began in February and broke down in May, and returning to negotiations on a political transition. These are reasonable goals, which are also embodied in a United Nations Security Council resolution adopted last December.
But a leaked text of the proposed agreement with Russia shows that it is riddled with dangerous loopholes. American and Russian representatives are now delineating areas where the Nusra Front is "concentrated" or "significant" and areas where other opposition groups dominate but "some possible Nusra presence" exists. This will still allow Mr. Assad and his Iranian and Russian backers to attack the non-Nusra opposition in those areas, as well as solidify the Syrian government's hold on power.
More worrying is that the Assad government lacks the manpower to hold rural Sunni areas and so will rely on Hezbollah and other Shiite militias to do so. These brutal sectarian groups will most likely force the Nusra Front and other Sunni rebels to decamp to Turkey, bringing them, and the threat of militant violence, closer to the West. The fighting will similarly displace Sunni civilians, leading more of them to try to make their way to Europe.
The administration's initiative with Russia is driven by either hope or desperation, but surely not by experience. During the partial truce, Russia took advantage of similar loopholes that permitted it and the Assad government to keep fighting the non-Nusra and non-Islamic State opposition. Such violations have allowed Mr. Assad and his allies to gain territory and besiege Aleppo.
The Obama administration appears to believe that President Vladimir V. Putin is looking for a way to limit Russia's involvement in the Syrian civil war. We doubt it. Mr. Putin is more interested in demonstrating that Russia and its friends are winning in Syria and the United States is losing. He will not alter his approach unless he becomes convinced that it has grown too expensive. Instead, because Mr. Putin knows the United States will not take action to punish Russia for its support for the Assad government, he and Mr. Assad will probably treat the emerging agreement no differently from the previous ones.
There is an alternative: Punish the Syrian government for violating the truce by using drones and cruise missiles to hit the Syrian military's airfields, bases and artillery positions where no Russian troops are present.
Opponents of these kinds of limited strikes say they would prompt Russia to escalate the conflict and suck the United States deeper into Syria. But these strikes would be conducted only if the Assad government was found to be violating the very truce that Russia says it is committed to. Notifying Russia that this will be the response could deter such violations of the truce and the proposed military agreement with Moscow. In any case, it would signal to Mr. Putin that his Syrian ally would pay a price if it did not maintain its side of the deal.
If Russia does want to limit its involvement in Syria, the threat of limited strikes should persuade it to make Mr. Assad behave. Conversely, if the skeptics are right that Mr. Putin will get serious about a political solution only if he sees the costs of backing Syria's government increasing, the threat of such strikes is probably the only way to start a political process to end the war.
Mr. Obama and Mr. Kerry have long said there is no military solution to the Syrian conflict. Unfortunately, Russia and Iran seem to think there is -- or at least that no acceptable political outcome is possible without diminishing the rebels and strengthening the Syrian government. It is time for the United States to speak the language that Mr. Assad and Mr. Putin understand.
Dennis Ross is the counselor and William Davidson Distinguished Fellow at The Washington Institute and former senior Middle East advisor to President Obama (2009-2011).
Andrew Tabler is the Martin J. Gross Fellow in the Institute's Program on Arab Politics.