Is ISIS Islamic?

I was pleased when Bush 43 said that the 911 terrorists did not represent Islam.

I was pleased when Obama and Cameron said similar things.

We don't want to be at war with Islam (or sometimes "1.6 billion Muslims").  It was appropriate for us to give a great religion the benefit of the doubt.

But I think that that has been said enough - by us.  If we keep saying it, then it relieves the folks in Tehran, Cairo, Saudi Arabia and such places from having to make that argument. It lets the leaders of Islam off the hook that their particular crazies have put them on.

I understand some muslim leaders in the US have issued a fatwa condemning the ISIS movement.  That is their job - to guide their flocks and tell the world that they are not all terrorists.

So I'm ready for Obama to quit saying things like:    ISIL (sic) is not "Islamic." 

(Which is a step beyond the previous statements above.)

How does he know that they are not Islamic?
They say they are Islamic.
How did Obama get to be the arbiter of who is and who is not Islamic?
If ISIS is not Islamic, why doesn't the much talked about "1.6 billion Muslims" step up and smash the 32,000 imposters who are ruining their good name?