America has no stomach for loss of life and treasure.
ISIS does, and that is their huge advantage. They know they simply need to outwait us.
ISIS is essentially a death cult- that wants to provoke a 'final solution' every bit as much as HB does.
ISIS wants European boots on the ground so that they can frame the war as Christianity versus Islam- and want to be leading Muslims to the final battle against the Infidels.
I agree with the others that have mentioned it- the solution has to be solved by the Middle East themselves- only other Muslims can ultimately defeat ISIS. We can help- as we are now- but until Turkey is more interested in defeating ISIS than defeating the Kurds, and Iraq wants to defeat ISIS more than it wants to defeat it's political rivals in Iraq, and Saudi Arabia wants to defeat ISIS more than promoting Wahabism, etc, etc.
A coalition of Turkey, Egypt, Jordan, Iran and Kurds could defeat ISIS and dig them out with no real place to hide.
But they are willing to let the U.S. and Russia get bogged down in that crap instead.