In response to a question from Al-Monitor, Saab said he would brief the results to the Barack Obama administration and others. Seven currently serving US officials were among those who participated in the exercise. Their identities could not be revealed under the ground rules of the game.

“We need big-ticket items,” Bilal Saab, a senior fellow at the Scowcroft Center, said Oct. 15 at a public event that disclosed some of the findings of the game.

There was also talk of creating a haven for displaced Syrians near the Turkish border, although some participants worried that this would be complicated by Russia’s recent military escalation and Turkey’s anxiety about steps that could strengthen Syrian Kurds.

The third and final phase of a war game, organized by the Brent Scowcroft Center on International Security at the Atlantic Council, examined three scenarios for dealing with IS: stay the course, diplomatic surge and heavy military intervention. The consensus was that the United States should adopt a hybrid of the last two options, including an effort to revive the stalled Geneva process, this time with Iranian participation.

WASHINGTON — A gathering of 50 current and former US officials plus regional and security experts concluded Oct. 14 that the United States should intensify both its diplomatic and military involvement in Syria to degrade and ultimately defeat the group that calls itself the Islamic State (IS).

Several participants besides Saab discussed the findings publicly.

Erin Simpson, a former adviser to US forces who is now CEO of Caerus Associates, a consulting firm, said Russia’s bombing campaign in Syria had helped change the focus for US policy analysts from Iraq — where the fight against IS appears to have stalled — back to Syria and the need to end that country’s 4-year civil war.

“US strategy has been a counterterrorism strategy and an Iraq-first strategy,” she said, “but the Russian intervention has brought the conversation back to Syria.” The US-led coalition no longer has “the luxury anymore of punting” on Syria, Simpson added. She said a diplomatic strategy would need to include “all the reputable players” and that the fate of President Bashar al-Assad would have to be addressed.

Another participant, Hassan Hassan, a fellow at Chatham House in London and co-author of the book "ISIS: Inside the Army of Terror," suggested a gradualist approach that emphasizes local cease-fires such as one mediated by Iran that briefly pacified the town of Zabadani over the summer. He said that IS is focused on entrenching itself in areas under its control through various means, including resolving disputes among local tribes. While acknowledging the impact of US airstrikes in containing the spread of IS in both Iraq and Syria, Hassan said the strikes are also having the counterproductive effect of destroying local economies and forcing residents to send sons to join IS for lack of a viable economic alternative.

With Russia increasingly involved in the war — albeit concentrating on non-IS opponents of the Assad regime — Hassan predicted that IS would seek to capture a Russian and kill him in a graphic and shocking way to boost recruitment of more foreign fighters. He added that IS would also seek to “drive a wedge between the US and Turkey” by conducting terrorist attacks in Turkey and “leaving a Kurdish calling card.”

The war-gamers agreed that the United States should do more militarily and not leave the field to the Russians.

“If the US and its partners and allies want to play a role, they need more leverage and that means more significant military investment to provide incentives for Assad and his allies to come to the table in a meaningful way,” said Barry Pavel, director of the Scowcroft Center.

Hassan called for more support for the Free Syria Army and elements of the group Ahrar al-Sham, which he said is “moving toward moderation.”

Simpson said a way also had to be found to acknowledge the strength of Jabhat al-Nusra, an al-Qaeda affiliate in Syria that has been fighting both IS and the Assad regime.

The Obama administration, while stepping up deliveries of arms and other material to the Kurdish PYD and affiliated Sunni Arabs in northern Syria, has abandoned a half-million dollar effort to train and equip a new rebel army and seems leery of more direct US military involvement.

Speaking on the same day that Obama announced that nearly 10,000 US forces will remain in Afghanistan to keep that country from falling to the Taliban and other Sunni extremists, Saab predicted that the administration will “most likely stay the course” in Syria and Iraq until Obama leaves office in 2017.

The issue of creating a no-fly zone in Syria has been debated both inside and outside the US government for years and has taken on new urgency with the rising numbers of Syrians displaced by the conflict and seeking refuge in neighboring states and Europe. Democratic presidential contender Hillary Clinton, who favored such a haven when she served as secretary of state in Obama's first term, said in a debate on Oct. 13 that she remains in favor.

While Russia’s activities in Syria “complicates that immensely,” Simpson said that establishing such a zone remains “an active topic of discussion at the worker bee level” in the US government.

Frederic Hof, a former State Department official dealing with Syria and another participant in the war game, told Al-Monitor that creation of “an aerial exclusion zone, a no-bombing zone or whatever” is necessary to stop the Assad regime from killing civilians with barrel bombs.

“This is a tactic that murders indiscriminately and makes the case for ISIS among Syrians desperate for protection,” Hof said, using an alternate acronym for IS. “It also boosts ISIS recruitment around the world. Is it possible under current circumstances to end or at least significantly curtail regime barrel bombing? Yes. Might it require an increased risk of confrontation with Russian military aviation? Yes it might, depending on the methodology selected. Are we serious about degrading and defeating ISIS? If we are, we’ll accept a degree of risk and put the Assad regime out of the ISIS-enabling, barrel-bombing business.”

Editor's note: The author, a senior fellow at the Atlantic Council, participated in the war game.