Foundational to Trumpism is the idea that Islam and democracy are incompatible, so Muslims can never be true members of western, industrial states — which is precisely what Isis believes about Muslims.
When Trump denounced the Gold Star mother and father of Army captain Humayun Khan, he doubled down on this idea that Muslims can never be integrated into western societies.
This is the message that Isis sends to the young people in the west whom they hope to win over to their side. It's why Isis (and al Qaeda before them) encouraged and participated in senseless attacks against civilians in western countries and cheered on the racist crackdowns that followed, since each attack proved their point: Muslims have no place in the west, and only one can prevail.
It's not a new tactic: the Stalinists of the early 20th century called it sharpening the contradictions, the idea that fence-sitters could be swayed to their side through the provocation of attacks on moderates.
A few days after Khan's speech, ISIS released its own view on the controversy in its online magazine Dabiq. Under a picture of the grave of Humayun Khan's grave at Arlington Cemetery, a caption wrote simply, "Beware of dying as an apostate." According to the worldview of Islamic State, Muslims of any denomination who do not accept its rule — let alone those who join groups like the U.S. military — are considered traitors. Not only have they forfeited their Muslim identity, they are considered contemptible enough for their deaths to be mocked and celebrated.
DONALD TRUMP AND ISLAMIC STATE AGREE: NO ROOM FOR PEOPLE LIKE KHIZR KHAN [Murtaza Hussain/The Intercept]