He can promise that all he wants, but that would indeed be a direct attack upon the Constitution of the US, in the US, and therefore a true reason to fight such Islamic extremism in the US itself. And in that case the extremists would lose big time. Remember what happened to Japan for doing the same thing?
However, in that case we would have even less incentive to invade their own country, which allows them the moral high ground, and increases our costs immeasurably! Why not just allow them to live in the paradise (He%%) that they think they can create in their own countries, they deserve just what they get!!