A year-long U.S.-led air campaign against the Islamic State has failed to reduce the size of the terror army, and its fighters remain in control of key cities, raising concerns the war is at a "stalemate."

Top officials in the Obama administration and on Capitol Hill are sharply at odds over the state of the U.S. mission today. Senate Armed Services Committee Chairman John McCain, R-Ariz., said recently that "ISIS is winning." The president's special envoy to the 62-nation counter-ISIS coalition says ISIS is losing.

Yet another official, the nominee to lead the U.S. Marine Corps, says the war is essentially a tie. Under questioning by McCain, Lt. Gen. Robert Neller said he does not believe ISIS is winning or losing.

"I believe they are in a stalemate right now," Neller said.

By the numbers, little has changed in the ISIS force size. A year after the U.S.-led air campaign began on Aug. 8, 2014, U.S. intelligence estimates ISIS has 20,000-30,000 fighters, the same number of fighters the CIA estimated last September. The unchanged estimate, first reported by the Associated Press, was confirmed to Fox News by a senior military official.

Asked about the estimates at a press briefing Tuesday, Pentagon spokesman Capt. Jeff Davis said he did not have the latest figures but did not dispute the numbers.

The White House defended its strategy on Monday.

"We have seen significant progress in terms of rolling back ISIL gains inside of Iraq, and the latest statistic is that up to 25 percent of the populated area that was previously controlled by ISIL is now [an area] where ISIL can no longer enjoy freedom of movement," White House Press Secretary Josh Earnest said, citing data the Pentagon announced in April.

Despite calling the war against ISIS a tie, Lt. Gen. Neller said he would not change the current strategy.

"I think we're doing what we need to do right now," he said.

Neller, like other senior military officers and administration officials, believes Iraqis must ultimately retake the cities lost to ISIS over the past year.

"They're the ones that are going to have to do this," Neller told McCain.

"General, they can't do it themselves, we know that, the Iraqis cannot do it themselves. That is why they are losing," McCain shot back.

A year into the campaign, the administration still cannot decide what to even call the enemy: ISIL, ISIS, Islamic State or Daesh.

But defenders of the strategy cite progress.

"I do believe that Daesh's momentum has been checked strategically, operationally, and, by and large, tactically," retired Marine Gen. John Allen, the president's envoy to the anti-ISIS coalition, said recently at the Aspen Security Forum.

As of Aug. 1, the U.S. military has carried out 4,563 airstrikes in Iraq and Syria, or about 78 percent of the coalition's 5,827 airstrikes. Of the nearly 9,000 targets destroyed, the list contains hundreds of armored Humvees and tanks -- originally gifts from the U.S. military to Iraq when it withdrew in 2011.

The U.S. military has trained 11,000 members of the Iraqi security forces. In June, President Obama approved a Pentagon recommendation to send 450 additional troops to the al-Taqaddum Airbase outside of Ramadi to train more Iraqis and reach out to local Sunni tribesmen, who once allied with the U.S. to defeat ISIS's predecessor Al Qaeda in Iraq.

But in Syria, finding a capable ground force has been more challenging. Unlike the 11,000 Iraqi troops trained by the U.S. military in Iraq, in Syria the number is much smaller.

Defense Secretary Ash Carter told lawmakers recently that only 60 Syrian fighters were being trained by the U.S. military.

A portion of those 60 fighters, known as the New Syrian Force, since graduating from U.S. training have made their way into Syria to battle ISIS. But Syria is littered with differing factions, including a number of Islamist groups battling the Assad regime. On Friday, the New Syrian Force found itself in a gun battle with Al Qaeda's Syrian affiliate, Jabhat al-Nusra. There were numerous reports that the leader of Division 30, which contained members of the U.S.-trained fighters, was abducted. The Pentagon and State Department could not confirm those reports. A senior military official, though, confirmed that five U.S.-trained rebels were captured by al-Nusra.

The Pentagon did confirm Monday that U.S. airstrikes supporting the handful of U.S.-trained rebels against al-Nusra took place last Friday. This comes on the heels of a policy shift in which the Obama administration will allow the U.S. military to take "defensive" action to support its trained force against not only ISIS, but al-Nusra and the Assad regime. For the first time, armed drones began flying out of Turkey over the weekend, according to the Pentagon.

Critics of the Syrian train-and-equip program say it was launched too late. Ambassador Frederic Hof, a senior fellow at the Atlantic Council and a former adviser on Syria to Obama, recently said the president did not accept a recommendation three years ago for more support to raise an army of 50,000.

Meanwhile, in the past year, the Islamic State has captured Ramadi, the capital city of Sunni-majority Anbar Province. Mosul, Iraq's second-largest city, also remains in firm control of ISIS despite initial plans to launch an offensive in the "April, May timeframe" -- a period long since passed.

In other areas of Iraq and Syria, ISIS has been rolled back. In March, the coalition took back Tikrit, with help from Shia-led forces, some allegedly backed by Iran.

Today, along the 560-mile Turkish-Syrian border, only 68 miles remain in ISIS controlled hands, according to senior administration officials. This comes as ISIS has been rolled back from the strategic border towns of Kobani and Tal Abyad, which has hurt ISIS' ability to resupply its de factor capital of Raqqa. On July 4, U.S. airstrikes bombed a number of bridges leading into Raqqa, further hampering the group's movement. The U.S. appears to have found a capable ground force in northern Syrian among its Kurdish fighters, some of whom coordinate airstrikes directly with the U.S.-led coalition.

Finding a capable ground force elsewhere in Syria and Iraq to combat ISIS has been challenging. After the fall of Ramadi in May, Carter questioned the Iraqi military's "will to fight" after a numerically superior Iraqi Army retreated to ISIS.

The outgoing head of the U.S. Army believes the U.S. and its allies will not defeat the Islamic State anytime soon.

"I think it's a 10-year problem at least. It's a problem that's gonna be there for a while," Army Chief of Staff Gen. Raymond Odierno told Fox News' Jennifer Griffin.