On Sunday, the already-awful situation in Syria got much, much worse. Al-Qaeda's faction in Syria, Jabhat al-Nusra, routed two major US-backed rebel groups, leaving al-Qaeda much stronger and US-backed rebels much weaker. Nusra even captured the rebels' advanced American weaponry — much as ISIS did during its rampage through Iraq in June.

These groups were supposed to be the great hope of America's strategy in Syria. That they were defeated so roundly and so soon after the US began implementing its new anti-ISIS strategy is proof positive of a wider truth: America's strategy for Syria has already fallen apart. Despite a spate of ISIS setbacks in recent months, America's effort to defeat ISIS in Syria appears to be making negative progress. Part of what's driving this is that every other available option is terrible, forcing the US to stick with a losing strategy that it knows well is losing.

A major defeat for Syrian rebels, and for the US strategy

Harakat Hazm and the Syrian Revolutionary Front (SRF) are two American backed Syrian rebel groups that are fighting three adversaries in northwestern Syria: the Bashar al-Assad regime, al-Qaeda's Jabhat al-Nusra, and ISIS. Both groups have been highly praised by Western observers. One influential DC think tank called Harakat Hazm "a model for the type of group the United States and its allies can support with meaningful, lethal military assistance," while the SRF has been called "the West's best fighting chance against Syria's Islamist armies."

These sorts of group are absolutely crucial for the US strategy in Syria. Just bombing ISIS can push it back only temporarily; there needs to be someone on the ground to actually take and hold the territory, or ISIS will just move back in. That's what these rebels were supposed to do in Syria's strategically crucial Idlib province, in the northwest.

On Sunday, both US-backed groups surrendered to Jabhat al-Nusra in Idlib after being routed in battle. The loss shattered the US strategy in northwestern Syria.

Idlib provence, whose capital city is circled in red on the above map, was the last northern province where moderate Syrian rebels had a large presence, according to the Washington Post's Liz Sly. This is important for America's anti-ISIS strategy because ISIS doesn't have much of a presence in the south, where rebels are mostly fighting the Assad government. Without strong US-backed rebels in the north, then, there's just no one well positioned to fight ISIS there — except for al-Qaeda and perhaps the Assad government.

This defeat could also deter other potentially pro-US rebel groups from working with the Americans. Jabhat al-Nusra appears to have turned on the SRF and Harakat Hazm specifically because they accepted American aid (at least in part). What rebel group would want to work with the US and thus invite Jabhat al-Nusra's rage? Why not, they must surely be asking themselves, work directly with Jabhat instead, as a number of rebel groups already do?

The Free Syrian Army, a rebel umbrella group that coordinates among various factions, is already unlikely to cooperate with US against ISIS; they're furious at the United States for refusing to take on the Assad regime as well.

All of America's alternative Syria strategies are terrible

The core of America's strategy — to build a coalition of moderate Syrian rebels to combat ISIS — is in really bad shape. Part of what makes that so discouraging is that the alternative options are terrible.

Simply bombing ISIS, and not seeking out a ground ally in Syria, would be folly. It's too easy for ISIS to hide from airstrikes within populated areas. Only ground troops, working with local civilians, could push them out.

As long as ISIS can safely retreat to Syrian bases, it'll be hard to beat them in Iraq

Some observers in the US have suggested allying with Syrian leader Bashar al-Assad against ISIS. It's more than possible that Obama will choose this: Assad has clearly signaled he's open to American support. But it'd be a strategic and moral disaster. It's not clear that Assad's Alawite-minority regime has the ability, or even the desire, to push ISIS out of the heavily Sunni regions it controls. Even if he did, it's not clear that Syria's Sunni majority would accept his rule — the fact that they didn't is part of how this conflict got started in the first place. And a US alliance with Assad would make the United States complicit in his absolutely brutal slaughter on Syrian civilians, inviting rage at the US — and perhaps implicitly encouraging Assad to be even more brutal.

The only other ground presence in Syria that the US could side with is Jabhat al-Nusra, which is already essentially at war with ISIS. But al-Qaeda's Syria branch is, if anything, more of a threat to the United States than ISIS is. No matter who wins that fight, the US loses.

A third option is to simply give up on trying to root ISIS out of Syria, instead focusing on defeating the group in Iraq. According to the Washington Post's Rajiv Chandrasekaran, that's already what America's strategy has become. Citing senior Obama officials, Chandrasekaran reports that American airstrikes in Syria "are not designed to push out the militants but to destroy the infrastructure, sources of revenue and command structure that have enabled them to operate successfully in Iraq."

This might actually work at achieving its relatively narrower aims; the US is making some solid gains weakening ISIS in Iraq. But as long as ISIS can safely retreat to its Syrian territory, it'll be very hard to beat them in Iraq. As Yale University counterinsurgency expert Jason Lyall puts it, citing his own statistical research: "one of the best predictors of insurgent success that we have to date is the presence of a rear area."

Moreover, it would mean admitting that Obama's strategy will not succeed in defeating ISIS. It would mean leaving Syrian civilians at ISIS's mercy. And it would allow the group a base from which to threaten the United States.

The collapse of America's Syria strategy was utterly predictable

The very nature of the Syrian war makes it almost immune to constructive American intervention.

First, it's important to understand that Syria's war is about much more than ISIS, and solving ISIS would require solving the larger Syrian conflict, which is just about impossible. The Syrian civil war grew out of a peaceful uprising against Assad, Assad's brutal crackdown against civilians, and the subsequent movement of grassroots rebels and defected soldiers to fight back. That turned into chaos, which ISIS and al-Qaeda took advantages of to establish new bases in Syria.

This means that unless the United States is somehow able to end that larger Syrian civil war, ISIS and al-Qaeda will have a base of operations. Furthermore, both Syrian rebels and Assad see one another as much greater enemies than ISIS, so they focus on one another. And from the rebels' point of view, turning their efforts against ISIS and al-Qaeda would be suicide. They're already struggling to hold out against Assad; taking on a secondary enemy like ISIS would spread them thin and likely doom them.

Free Syrian Army officials have repeatedly said that the US could solve this crisis by taking on both ISIS and Assad, thus giving Syrian rebels a reason to fight on the US's behalf. But that would take an absolutely enormous American military effort, possibly including a ground invasion and occupation. The Obama administration is understandably unwilling to repeat the 2003 Iraq war in Syria. The Iraq war proved, among other things that an American invasion, wouldn't guarantee that Syria would be better off afterward.

So the US strategy against ISIS in Syria was doomed to collapse almost from the get-go. Those Syrian rebels who joined up with the US effort anyway have become targets for al-Qaeda, ISIS, and Assad, each of which has their own reasons for wanting to obliterate US-backed rebels. They're paying the price for America's failure in Syria.