Imagine that the American right decides to make, say, ISIS "their issue", which leads the left wing to engage in denialist tactics.

That is, the American left denies ISIS. The refuse to accept such a group exists.

Sure, some people make the claim, but it's all theory (and some Youtube videos), and there are alternative explanations.

In such a case, would you say the problem begins with the American right making it "their" issue?