Joint Chiefs of Staff

Mosul is more than a potentially climactic military battle

More is riding on the battle for Mosul than the recapture of the Islamic State group's main stronghold in northern Iraq. Also on the line is the Obama administration's theory that the extremists can be defeated in Iraq, Syria and elsewhere without American ground troops doing the fighting.

For more than two years, the administration has stuck to its argument that the only path to a sustained victory over the Islamic State group is for locals, not Americans or other outsiders, to bear the main responsibility for the fighting and for governing after the extremists are removed.

President Barack Obama has taken a lot of political heat for that approach, which critics say has...