In U.S., growing skepticism over "no boots on ground" war plan

Obama’s repeated vow that he will not order “boots on the ground” has infuriated Republicans in Congress, who argue that air power alone cannot roll back the IS extremists given the absence of a viable moderate rebel force in Syria and the Iraqi army’s poor track record.

Their view has been reinforced by former US commanders who question the idea of openly ruling out the use of ground troops, saying it could signal weakness to both adversaries and allies.

Retired Marine general James Mattis, the blunt-talking former head of US Central Command, told lawmakers Thursday you should not “tell your adversary in advance what you are not going to do.”

“The fewer restrictions we place on ourselves going into this, the more apt we are to see other nations give their full measure,” Mattis told lawmakers.