He’s an ignoramus on the subject who thinks that, e.g., references to alleged warming on Mars somehow genuinely undercut the credibility of mainstream climate science.
Now mind you, there are many other politicians who are no better than Thompson in this regard. But none of them deserve the noble title of “sceptic” (or “skeptic” as we tend to say here), in the sense of a knowledgeable person who reserves judgement in the face of factual uncertainty. They aren’t even informed enough to be genuinely skeptical.
Certainly: it’s a lie, or at best a deliberate half-truth. The early American legislators were attempting to protect both the church from the state and the state from the church. As we see, for example, in the Constitutional provision that no religious test of any kind may be required for a holder of elective office.
[In preview: and what BG said.]