According to a report in Politico, senior U.S. military leaders are dubious of getting involved in a major war against ISIL. They don't doubt our capability to do kinetic damage, but they question our ability to control the aftermath. Obliterating ISIL doesn't solve the Shia/Sunni/Kurd clashes in Iraq, or the civil war in Syria -- or the ISIL-linked or -inspired forces in Yemen, Libya and elsewhere.
What's more, the Iraqis don't want a large U.S. fighting force back in their territory.
I'm sure some military planners can provide options for civilian leaders; they never say they can't do anything useful. But whatever they may suggest still has to be put in the context of what else? what next?