Demonization is when you generalize from some bad things a person does, such as trying to defund and suppress climate research, and attribute it to the person being an essentially bad person who naturally gravitates towards evil in everything. An example of demonization would be if I said Jim Bridenstine consistently works to suppress climate science, therefore he must like human suffering, hmmm, makes you wonder if he likes rape. That's demonization. Saying he's an enemy of climate science, and also that he has incorrectly cited science as proving that gay couples don't make good parents, and that I think these are horrible things, is not demonization.

As for ad hominem, talking about Bridenstine's politics is not an irrelevant aspect of the debate, like if I said he was stupid or a bad soccer player. In fact, they're the only thing that matters. Bill Nye is attending as Jim Bridenstine's formal guest to a government event, a gesture of personal support of Bridenstine in his capacity as a government official, so what Bridenstine does in that capacity is important for interpreting the meaning of Bill Nye's attendance.