Underscoring the multiple challenges facing his administration, President Barack Obama consulted with military officials Wednesday at MacDill Air Force Base about the U.S. counterterrorism campaign against Islamic State militants.

Obama met with Gen. Lloyd Austin, who will oversee the military campaign against the Islamic State group as the head of U.S. Central Command, and other military officers to discuss operational details.

U.S. military efforts in the Middle East are directed from MacDill's U.S. Central Command.

Accompanying Obama were his national security adviser, Susan Rice, and Defense Secretary Chuck Hagel.

Obama addressed Central Command troops, providing him another opportunity to make a case for the air strike campaign he wants to carry out against Islamic State.

The President also thanked troops for their service.

"You play a central role in our combat and counterterrorism efforts," Obama told the MacDill troops. "Your work is as vital as ever. In an uncertain world, full of breathtaking change, the one constant is American leadership.

"It is America that has the capacity and the will to mobilize the world against terrorists, including the group in Iraq and Syria known as ISIS."

The president said the fight against the Islamic State group cannot be America's alone and will require a broad coalition. He said some nations will assist the U.S. with airstrikes and others will help train forces.

Obama spoke for 15 minutes. Then, servicemen and women rushed to shake the President's hand, encouraged by his visit.

“It's good to know that he supports us and we are here to do whatever he needs us to do,” said Lt. Claudia Rivas.

His meeting with top U.S. commanders comes amid newly raised doubts about the ability of the United States to rely on Iraqi forces, Kurds and Syrian opposition fighters to carry out a ground fight against the Islamic State militants and whether U.S. troops might have to play a combat role.

It also comes as Congress prepared to vote on Obama's request for authority to equip and train Syrian opposition fighters whom the administration deems as moderates in the Syrian civil war.

Lawmakers in both parties have raised worries that the U.S. might be unable to find enough Syrian rebels who could be trusted to confront the Islamic State or that their numbers would be sufficient against the extremists.

Army Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, raised new doubts about Iraq's role in the fight, telling a small group of reporters traveling with him to Paris that about half of Iraq's army is incapable of being an effective partner with the U.S. to push the Islamic State back in western and northern Iraq. He said the other half needs to be partially rebuilt with U.S. training and additional equipment.