Top U.S. military leaders faced skepticism Thursday on Capitol Hill as they made the case that President Obama’s strategy in Iraq and Syria is beginning to show results against the Islamic State.

Appearing before the Senate Armed Services Committee, Defense Secretary Ashton B. Carter and Gen. Joseph F. Dunford Jr., chairman of the Joint Chiefs of Staff, described growing momentum against the group, which has lost ground to U.S.-backed fighters in Syria and Iraq in recent months. Carter and Dunford also outlined new military measures designed to make local forces more effective.

In the past two weeks, Obama has approved plans to allow American advisers to accompany local troops closer to the front lines in Iraq, and the use of attack helicopters and long-range artillery in a highly anticipated offensive to recapture the northern city of Mosul. In Syria, the president substantially increased the size of a Special Operations advisory force, which officials say in recent months has made headway in identifying and bringing together local forces that may eventually be able to press into the militant stronghold of Raqqa.

The U.S. strategy centers on equipping and advising partner forces in both countries while using American air and artillery support to help those forces advance into well-defended militant areas.

“The bottom line is this: We can’t ignore this fight, but we also can’t win it entirely from the outside in,” Carter told lawmakers. “That’s why we’re helping capable, motivated local forces in every way we can, without taking their place.”

Armed Services Committee Chairman John McCain (R-Ariz.), a prominent critic of Obama’s foreign policy, said the White House had acted too cautiously as the Islamic State gained strength, and more recently misjudged the ability of Russian President Vladimir Putin to alter the course of the Syrian conflict by throwing his military support behind the government there.

Although military leaders say they can now discern a path toward crippling the group in Iraq, the outlook is much more gloomy on Syria’s multi-sided civil war. A cease-fire reached in February now appears to be on the brink of collapse, while Geneva peace talks between the warring parties seem stuck.

“Once again, the response has been reactive, slow and insufficient,” McCain said. “Despite the real tactical gains we’ve made, we must ask ourselves: Is this working? Are we winning?”

Other lawmakers, mostly Republicans, questioned the administration’s strategy, which remains focused on the Islamic State even as forces loyal to President Bashar al-Assad continue to launch attacks, resulting in civilian casualties. The Assad regime, backed by Iran and Russia, appears to be attempting to regain control of Aleppo, the country’s largest city.

Sen. Roger Wicker (R-Miss.) pushed Dunford on why Obama hadn’’t ordered the Pentagon to attack Assad’s air force, which the United States has accused of using barrel bombs with devastating effect. “The task he’s given us militarily is against ISIL,” Dunford said, declining to say whether the United States should take such action.

Sen. Dan Sullivan (R-Alaska) pressed the officials about Obama’s promise that U.S. troops would remain out of combat in Iraq and Syria. Since the beginning of renewed military operations in 2014, U.S. warplanes have conducted thousands of combat flights, and two U.S. military personnel have been killed in combat situations in Iraq. Special Operations troops also are conducting secret missions — which Dunford said were combat operations — against the Islamic State and other counterterrorism targets.

“Why does the administration go through these crazy somersaults, that the entire country knows is not correct, to say our troops are not in combat when they’re in combat?” Sullivan asked.

A senior administration official, speaking on condition of anonymity to address U.S. policy in Iraq and Syria, said the mission did include “limited operations” against the Islamic State. “This is very different from the combat mission with forward-deployed maneuver forces of the type we previously conducted in Iraq,” the official said.

Addressing the growth of the Islamic State beyond Iraq and Syria, Dunford and Carter said the United States is preparing for possible action against the group’s Libya affiliate, its most important one. Without giving details, Dunford said that Gen. David Rodriguez, the head of U.S. Africa Command (Africom), had prepared plans to support local forces in Libya.

He said the Pentagon had recently reassigned military assets to Africom — presumably aircraft used for surveillance — to develop intelligence for future Libya operations.