Russia’s heightened military support to Syria has raised questions about Moscow’s intentions and whether it will help or thwart efforts to fight the Islamic State. The consequences, notes Paul Saunders, will depend on whether or not Washington and Moscow can find a mutually satisfactory way forward in the war-torn country.

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Russia’s dramatic recent increases in military support to Syria have produced considerable uncertainty regarding Moscow’s intentions. Will Russian forces engage directly in combat against the so-called Islamic State? Could Russia’s help allow the Syrian military to intensify attacks on “moderate” opposition groups? Or could it lead to accidental confrontation between Russian and American military personnel? And what will Moscow do next?

Moscow faces very substantial constraints, though, that are likely to impose important limits on its conduct. Russia’s actions will probably be much more consequential politically than militarily.

Mutually Reinforcing Objectives

President Vladimir Putin’s decision to send aircraft, armored vehicles, and naval infantry to Syria—and, apparently, to build at least one new base there—is likely the result of several mutually reinforcing objectives. Militarily, Russia seeks to avoid a victory for the Islamic State that would allow the extremist group to consolidate control over Syria’s territory and, no less important, that would release over 2,000 experienced and dangerous Chechen fighters from combat for potential return to Russia.

Unlike the United States and many of its allies in the region, Russia does not see the moderate Syrian opposition as a viable force that could counterbalance and eventually defeat Islamic State fighters. Since no one else (including the United States) is willing to provide a major ground force, and air strikes alone cannot defeat the Islamic State, Russian officials see Syrian President Bashar al-Assad’s army as an essential partner.

Politically, Russia’s leaders have sent several messages simultaneously. To the United States and its allies, Moscow is arguing for a significant role in any international coalition against the Islamic State and in any political process to establish peace. More narrowly, the moves looked calculated to force open military-to-military dialogue with Washington, suspended after Russia’s seizure of Crimea, in order to avoid accidents or miscalculations.

This has already partially succeeded in producing a telephone conversation between Secretary of Defense Ashton Carter and Defense Minister Sergey Shoigu. What remains unknown is whether President Barack Obama will agree to meet Mr. Putin during his visit to the UN General Assembly on September 28.

At the same time, Russia’s actions demonstrate to Bashar al-Assad and Syria’s generals that Moscow is committed, at least to some degree, to preventing their defeat. This gives Syria’s leaders a greater stake in their relations with Moscow. It could also help to reassure Mr. Assad and others of Russia’s intent in any international negotiations—something required to win the Syrian government’s support for any deal.

Political Constraints

Still, despite its military deployments, Russia lacks the capability to deploy, or to sustain, a large enough number of its own troops to make a difference in Syria’s bloody civil war. Russia’s “naval base” in Tartus, Syria, cannot accommodate large ships and is primarily a repair and resupply facility.

Though Moscow recently negotiated naval access to Cyprus, this is not sufficient either—soldiers and supplies would still have to travel by ship or by air to Syria. Supporting a meaningful force in Syria by air would be extremely expensive and logistically quite demanding. Taking into account the number of portable surface-to-air missiles in Syria, it could also be quite risky for Russian cargo pilots.

Russia faces similar political constraints. Most important, Russian public opinion remains deeply scarred by the Soviet war in Afghanistan and Russia’s two wars in Chechnya. Not unlike the American experiences in Vietnam and Iraq, these bloody conflicts—a defeat in Afghanistan and at best inconclusive in Chechnya—have produced a profound reluctance to fight in far-off lands. If Islamic State forces were to capture and publicly execute one or more Russian soldiers, as they have already done to others, President Putin could face an angry public with few credible policy responses.

The most important question following Russia’s sudden escalation in Syria is whether it may advance—or set back—wider efforts to thwart the Islamic State and reestablish stability. The answer to this will depend heavily on whether or not Washington and Moscow can find a mutually satisfactory way forward in Syria that facilitates not only their cooperation but also a new international coalition.

So far, the biggest obstacle to such an understanding is the long-standing US-Russian disagreement about President Assad. Washington views Assad’s behavior as a recruiting poster for the Islamic State, while Moscow considers his leadership necessary to preserving a unified Syrian state that can continue to fight the ground war. And, of course, President Obama has insisted that Assad must agree to step down as a pre-condition for talks. Moscow rejects this approach.

Some in Washington sound increasingly prepared to contain their distaste for Mr. Assad—and, for that matter, for Mr. Putin—at least for a time. Neither decision would be an easy one for the Obama administration, however, particularly as the 2016 electoral campaign heats up. Look to the White House for the next move.