There is a very simple reason that the Democrats refuse to credit Islam with being involved with ISIS or with terrorism generally: because they view Islam in the same way they view Christianity or Judaism, which is to say as a thing that you can mouth adherence to if it fits your personal or political ambitions, but not a thing that should actually exercise influence over your life. To most Democrats – elected Democrats in particular – religion is viewed with the same kind of casual contempt one would view membership in a particularly annoying and demanding social club.
Recall that Barack Obama’s entire defense during the 2008 campaign when the rhetoric of Jeremiah Wright began to be exposed was, essentially, “Well, you know, I haven’t actually been to church in years, so I missed all that.” And everyone basically said, “Ah, yeah, that kind of makes sense.” Ditto Hillary, who it is even hard to imagine singing along non-ironically with an organ and Sunday hymnal. Bernie Sanders, for his part, is pretty much openly agnostic.
Democrats have long viewed with suspicion and distrust anyone who takes their religion seriously. Anyone who believes that their religion ought to be the central organizing force in their life and acts accordingly is given the side eye by our elected betters in the Democrat party, who are fond of openly saying (especially in connection with abortion) that, hey, they love Jesus too, but let’s not get carried away with letting that matter.