There are still huge problems with the US strategy for fighting ISIS

The US is making significant gains in its fight against the Islamic State. But some are still skeptical of whether Washington's overall strategy is going to work in the long run.

The Islamic State (also known as ISIS, ISIL, and Daesh) has lost key territory along the Turkish border - a frontier that it uses to funnel foreign fighters into its territory - and near Raqqa, the capital of its so-called "caliphate." A US-led anti-ISIS coalition has been using air strikes in an attempt to cripple the terror group and to support local forces and militias fighting ISIS on the ground.

But the US still isn't meeting its capacity for training anti-ISIS fighters. And it's unclear how many Sunnis have joined the Iraqi security forces to retake territory from ISIS.

Sunnis are key to the US strategy. ISIS is a vehemently sectarian Sunni group, and most of the cities ISIS has seized and that US and Iraqi forces are preparing to retake, including the Baghdad suburb of Ramadi, are Sunni-dominated.

President Barack Obama said Monday that "more Sunni volunteers are coming forward," but did not say when they'll be ready to join an offensive on Ramadi or how many fighters are being trained, according to The New York Times.

The US is training an estimated 2,000 fighters total in Iraq right now. But US advisers and personnel have the capacity to be training 6,700, leaving a large gap while an often-dysfunctional Iraqi army is already spread thin defending other areas.

The US hasn't yet provided a timeline for the Ramadi offensive. The operation to retake Mosul, Iraq's second-largest city and another ISIS stronghold, will likely be shelved until next year, even though the US military originally planned for a Spring 2015 push against the city.

Richard Spencer, The Daily Telegraph's Middle East correspondent, pointed out the problems that are still present with the anti-ISIS coalition's strategy, calling the administration's view of Iraq "increasingly delusional":

As Spencer notes, the issue isn't just the numbers of troops the US trains in Iraq. There's also the disorganization of the Iraqi military itself. Department of Defense Secretary Ashton Carter said the Iraqi army lost the "will to fight" when ISIS stormed into Ramadi in May. Iraqi security forces withdrew in the face of truck bomb attacks despite outnumbering ISIS militants.

And Iraq's Shiite-dominated government doesn't seem willing to divert fighters from defending Baghdad to send them into Sunni areas. They're also reluctant to train and arm Sunni-organized defense forces over fears that even anti-ISIS Sunnis might one day rise up against Baghdad.

Consequently, the most effective fighting forces on the ground have been the Kurds - an ethnic group with longstanding tensions with the Baghdad government - and Shia militias backed by Iran. Sunnis with an incentive to defend their own territories have barely been relevant to the fight against ISIS.

So while the strategy of air strikes supported by ground forces might be successful in pushing back ISIS in the short term, the coalition gains could end up being "quick wins" that aren't sufficiently backed through a long-term strategy, as Shadi Hamid of the Brookings Institution's Center for Middle East Policy explained to The Washington Post.

"This is where the focus on quick wins becomes problematic," Hamid told the Post. "The US isn't thinking about what happens after ISIS is pushed out of an area."