They saw the ISIS attack coming—and they ran.

U.S. military officials believe that the city of Ramadi fell to the self-proclaimed Islamic State over the weekend in large part because the Iraqi security forces there fled in the face of an ISIS assault.

The American strategy to fight ISIS in Iraq depends on local troops standing up to the terror army. That Iraqi forces chose not to fight—much as they did last year when ISIS sacked the city of Mosul—reinforced how little the U.S. effort has bolstered Iraq’s security. The Pentagon has said it trained 7,000 Iraqi forces since Mosul’s collapse and launched more than 3,700 airstrikes, hitting 6,300 targets. In the month leading to Ramadi’s collapse, the U.S.-led coalition conducted 165 airstrikes in Ramadi alone, according to military statistics. And yet, once again, the Iraqis could not mount a defense against a charging ISIS.

The 6,000 Iraqi forces—plagued with poor equipment, bad resupply chains, and low morale—saw a series of ISIS attacks and 8 to 12 car bombs hit in Ramadi sometime Friday. In response, those troops decided to retreat to a position a few miles east and north, U.S. defense officials believe. That is, once confronted, the troops fled the fight.

The ISIS attacks were “enough to make the Iraqis believe they didn’t want to fight,” a defense official told The Daily Beast. “We’re still trying to figure out what flipped the switch.”

There are differences between how the Iraqi troops performed in Mosul and Ramadi, U.S. defense officials said. Iraqi forces held the city for more than a year, even as ISIS-controlled areas dominated the province. And while Iraqi troops stationed in Mosul last year were wearing civilian clothes under their uniforms, in Ramadi, they conducted a tactical retreat.

That said, they were a broken force—when they were supposed to be a keystone of the U.S. strategy in Iraq. Instead, the strong local ground force that the Pentagon hoped could exploit American air superiority over ISIS does not appear to exist within the Iraqi army.

“We don’t really have a strategy at all,” Robert Gates, President Obama’s former defense secretary, said Tuesday on MSNBC. “We’re basically playing this day by day.”

The Iraqi government seemed to recognize the limits of its forces as well, inviting Shiite militiamen on Monday to help their forces regain Ramadi. That won’t be an easy task. U.S. officials have said the airstrikes will only continue if those militiamen are under government control. And even if they are put under Baghdad’s aegis, General Martin Dempsey, the chairman of the Joint Chiefs of Staff, said in a statement Monday, it might not be enough. “Much effort will now be required to reclaim the city,” he said.

While U.S. military officials—including Dempsey—were keen to dismiss Ramadi’s tactical importance, its fall to ISIS hands over the weekend marked the biggest ISIS victory since the group claimed Iraq’s second-largest city, Mosul. Ramadi’s fall highlighted the limits of both the Iraqi military and a U.S. strategy that depends so heavily on them. Moreover, defense officials who measured success by how little ISIS could move or how much of the equipment had been destroyed were forced to concede such statistics were not an effective measure of the campaign against ISIS.

For those hoping more Sunnis would join the Iraqi-dominated Shiite military and government, the scene in Ramadi over the weekend of mass executions made that all but impossible, in the short term at least. ISIS fighters slaughtered Sunnis in Ramadi suspected of working with government forces, reportedly throwing bodies into the Euphrates River.

The city’s fall has also lead to a humanitarian crisis. According to the U.N., almost 25,000 residents have fled Ramadi, mostly toward Baghdad.

In addition to claiming the city, ISIS procured scores of U.S. tanks and artillery vehicles given to the Iraqi security forces.

As Army Colonel Steven Warren, a Pentagon spokesman, explained Tuesday: “Certainly preferable if [that equipment] was destroyed” before ISIS claimed Ramadi; “in this case, they were not.”

The city’s fall ended talk of going after ISIS-controlled areas like Mosul. Where just a few months ago, the U.S. military said the Iraqi forces could lead an assault on Mosul as soon as April, now there is talk of nothing happening until next year.

“Who knows if it will ever happen at this point,” a second defense official concluded, frustrated by events on the ground.

The collapse of yet another Iraqi city to ISIS raised new questions about the durability and effectiveness of the U.S. approach from Democrats and Republicans alike.

To the extent that the administration has been measuring success against the Islamist group by ticking off the number of airstrikes against ISIS positions in Iraq and Syria, as a White House spokesman did on Monday, “alarm bells should be going off,” Representative Adam Schiff told reporters Tuesday.

Schiff, the most senior Democrat on the House Intelligence Committee, called ISIS’s capture of Ramadi “a very serious and significant setback” in U.S.-led efforts to defeat the Islamist group. Schiff said that he didn’t think the U.S. was “losing the war” against ISIS, “but we’re not making tremendous progress, either.”

Meanwhile, Republican Senator Lindsay Graham (S.C.), a presumed presidential candidate, called for 10,000 U.S. troops to train the Iraqi forces faster and support Iraqi forces fighting ISIS. There are roughly 3,040 U.S. troops in Iraq, mostly assigned to train or work with their Iraqi counterparts at military headquarters in Baghdad and Irbil.

The Shiite militiamen, which are not under government control, along with Kurdish forces, known as peshmerga, appear to be the only troops that can sustain a prolonged battle for control of a city.

Both Iraqi forces and ISIS fighters have yet to hold a city after a long battle. When Iraqi and militia forces moved on the central city of Tikrit this month, ISIS forces eventually ceded ground. And when ISIS forces battled for the northern Syrian city of Kobani and Iraq’s Sinjar mountain, Kurdish forces wrested control away.

Even if Ramadi is eventually recaptured, it’s not clear how much of Anbar’s provincial capital will be left to claim. Kobani, for example, was kept out of ISIS hands, but what remains is the dysfunctional shell of a city, abandoned by residents. Seven weeks after the Iraqis heralded their win over ISIS forces in Tikrit, residents have yet to return as the Iraqi government has not yet been able to restore services like electricity, defense officials have said.

“What does taking back mean if it is going to look more like a war zone? And how will the Shiite militias behave once there?” one adviser to the U.S. mission in Iraq asked. “Eventually Ramadi will be taken. Whether the Iraqi forces can hold it is something else.”

—with additional reporting by Shane Harris