US warplanes continue to pound Mosul, the largest city in ISIS territory and the major prize Iraqi officials are constantly talking about retaking. Yet officials are heavily debating the timetable for retaking the city, and how difficult it will be.

ISIS has shown an ability to defeat Iraqi troops in head-on battles, even when backed by US warplanes, and the militants have had half a year to fortify Mosul, which they know is going to be attacked sooner or later.

US officials have downplayed the chances of Iraqi forces retaking the city on their own, and may be planning to use the importance of retaking it as an excuse to justify the use of US ground troops in direct combat.

The administration has repeatedly insisted they have no plans for ground combat, but Pentagon leaders have repeatedly said they may recommend a change under certain special circumstances. Mosul seems to be a tailor made circumstance.