The decision over which target to attack has deep implications in Washington and Baghdad. Attacking to the north, towards oil-rich Baiji, could keep the hard-won momentum against ISIS rolling, but any setback could be crushing for the still weak Iraqi forces. It would also leave Baghdad’s western flank exposed. Attacking Anbar instead would secure that flank, but could also stall the larger campaign, leave Kurdish troops and American fighter jets battling ISIS practically alone, while strengthening Iranian-backed militias’ influence in Baghdad.

Some U.S. military leaders argue for the first option, hoping to sustain the momentum of the March 31 win in the central city of Tikrit, the first major victory against ISIS. They want Iraqi forces  to keep heading north along the Tigris and clear the highway route toward Mosul, Iraq’s second largest city and the capital of ISIS’s Iraq caliphate. That highway runs along the Tigris.

Where U.S. officials once privately pushed to move north toward Mosul, they now are suggesting the next major city of Baiji, between Tikrit and Mosul. Only after Baiji, which at its peak was home to 200,000 residents, would U.S. military leaders recommend tackling Anbar province and then Mosul after that, two military officials told The Daily Beast.