One guy repeatedly argued against various Republican policies over the years, very rarely finding fault with Democrats. Yet he was one of the smoke/fire people in regard to Clinton.

Lots of people didn't trust her according to various polls.

I'm looking for psychological studies on this weird behavior (in another window), assuming it exists.

People's perception of motivation could play a role too. Going back to my former AA co-workers, they would also say things like, "Joe's just an ignorant redneck" to explain some of his racist comments.

https://www.washingtonpost.com/news/post-politics/wp/2016/10/04/as-clinton-recovers-in-polls-trust-issue-simmers/?utm_term=.a41bec984dcd

In the latest full Washington Post/ABC News poll, conducted before the first presidential debate, just 33 percent of voters called Clinton "honest and trustworthy," to 62 percent who said she wasn't. Forty-two percent of voters considered Trump trustworthy. After the debate, a follow-up poll found more voters believing she had told the truth. But among the voters who thought both Trump and Clinton had bobbled their facts, more voters thought Clinton had done so on purpose.