Don't believe for one minute the narrative that the USA is threatened by ISIS and seeks to destroy it. The real target is Assad's Syria, a Russian ally. (Why? some say that Assad/Russia is what prevents a gas pipeline running from Qatar to Europe but that seems farfetched to me).
The stupid concentration of NATO/Saudi forces plus Israel is going to provoke Russia and Iran to concentrate their forces there too. They are not going to let Assad get Gaddafied.
And the compelling national interest reasons for this buildup are nonexistent.