Iraqi politicians and military commanders have said repeatedly the self-proclaimed Islamic State’s grip on the city of Tikrit was about to end in the face of an overwhelming Iraqi military and militia offensive.

Just last week, Iraqi Prime Minister Haider al Abadi reportedly declared that victory was near and “achieved totally by Iraqi hands.” And in an interview with ABC’s This Week that aired March 8, the prime minister said the forces’ advances were “ahead of planning.”

But two Pentagon officials told The Daily Beast on Thursday that the fall of former Iraqi leader Saddam Hussein’s hometown was at least two weeks away, as the campaign now is “stalled.” As Army Col. Steve Warren, a Pentagon spokesman, told reporters Thursday, the Iraqi forces have not yet reached the center of the city.

The Iraqi forces are “on the outskirts of the city,” said Warren, and “they certainly have it surrounded.” But a siege in itself is no triumph.

So, how did the fall of Tikrit go from being inevitable to, now, a protracted fight?

Several reports cited the overly optimistic outlook from senior Iraqi leaders who repeatedly suggested the imminent fall of the central Iraqi city.

The numbers of troops involved suggested there was good reason for great expectations. U.S. officials have said roughly 20,000 Iraqi Shiite militiamen and 3,000 Iraqi troops along with Iranian fighters are confronting the terror group. And according to the two Pentagon officials, the U.S. estimates those 23,000-plus fighters are combating between 400 and 1,000 ISIS fighters in Tikrit. It is unclear how many of those have pulled out or been killed since fighting began, the officials said.

The ISIS forces in Tikrit have planted explosives and destroyed bridges, forcing Iraqi forces to clear out streets slowly and systematically, defense officials have said. In addition, ISIS appears to have destroyed the bridge over the Tigris River that leads to Tikrit, compelling Iraqi forces to travel 40 miles north to the next bridge, the two Pentagon officials said.

“That may not seem like much, but moving forces is a challenging undertaking,” one of the Pentagon officials explained. And with that, what was supposed to be a swift ISIS defeat slowed way down.

An ISIS loss in Tikrit would mark the biggest loss of terrain for the group since it stormed Mosul, Iraq’s second-largest city, last June.

Given that the group derives its power almost as much from perception as from feats of arms, such a loss could put a major dent in its quest to consolidate the territory of its so-called caliphate. It could also set back recruitment of foreign fighters coming to join ISIS, and worsen growing internal fractures about different strategies for the way forward.

“Tikrit is going to fall at some point. The question is how long can the Islamic State delay it. Every day they do, it is a win for ISIS because they are exposing the fundamental weakness of the Iraqi Security Forces and highlighting that this is an Iranian effort, not just an Iraqi one,” says Christopher Harmer, senior naval analyst with the Middle East Security Project for the Washington-based Institute for the Study of War.

Iraqi officials have not said how many troops have been killed in the battle for Tikrit but in a Washington Post report from the Shiite holy city of Najaf, where many troops and militiamen would be buried, cemetery workers said as many as 60 were dying daily.

How long the Iraqi forces will be willing or able to sustain such losses remains unclear.

In the last few days, as the Iraqi campaign bogged down, volunteers from various militias stationed in Baghdad and points south have moved in, including members of the Badr Brigades, the Peace Brigades, formerly known as Shiite rebel leader Muqtada al Sadr’s Mehdi Army, and the League of the Righteous, a splinter of the Mehdi Army.

As frustrations mount, so does the potential for an unrestrained and vengeful effort to crush the mostly Sunni city, which is still home to thousands of civilians. “Will they be willing to indiscriminately bomb them into submission?” one of the Pentagon officials asked.

Shortly after the Tikrit campaign began March 1, Pentagon officials cautioned that while Iraqi forces were moving in quickly from the northwest and southwest, they would inevitably face a tough fight from an ISIS unwilling to lose the last city it holds in Salahadin province. As the effort slowed, Pentagon officials called it a natural pause in fighting, but they now concede ISIS resistance has slowed the Iraqi plan.

In public statements and in congressional testimony, Army Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, has said the fall of Tikrit inevitable but also has called for “strategic patience.”

And where Iraqi officials once boasted of not needing U.S. help, in part because Iran had deployed advanced missile and rocket systems to Tikrit, some in the Iraqi government are now suggesting they need help from the airpower of the U.S.-led coalition.

Pentagon spokesperson Warren says that Iraqi officials have not “formally requested” the assistance of U.S. airpower.

The U.S.-led coalition effort has notably steered clear of Tikrit as Iraqi forces are bolstered by Iranian weapons, tanks, advisers and troops, and the presence of Gen. Qassem Suleimani, the leader of Iran’s expeditionary Quds Force.

What coalition airstrikes throughout Iraq and Syria have done, however, is make it all but impossible for ISIS to send in a large formation of forces to bolster its presence in Tikrit. As of March 18, the U.S. and its allies in the coalition had struck 5,314 targets in Iraq and Syria, the Pentagon said Thursday.

Pentagon officials are watching the Tikrit operation closely to see what lessons may be learned before a major effort to reclaim the much bigger prize of Mosul. And one of those lessons already is clear: It won’t be easy.