Related to this, there is probably a psychological effect at play where people want to be consistent with what they have said in the past (see Cialdini and consistency theories), so just the act of asking the research participants to articulate their feelings about the person dug themselves into a hole. Talk less and you don't have to entrench.

I apologized in a meeting yesterday when I realized I said something factually incorrect. I actually fact checked myself to discover the error. I wonder if that was a mistake. Given how our leaders act, I think we are more wired to trust people who never acknowledge their mistakes.

What is a stupid person?

For purposes of these discussions, it is always conflated with "right of center". Academics accept this as a forgone conclusion, or, at best, use some self-referential circular argument for why the conservative political allegiance is the domain of the less-enlightened, e.g., fewer conservatives went to institutions that are overwhelmingly liberal for career training (university, especially when advanced degrees are considered), or fewer white-collar workers are willing to express conservative views. Neither of these things have much of anything to do with intelligence or stupidity.

Rest assured, there are plenty of blistering idiots on both sides of aisle, in equal proportions that match the idiocy of the general public (roughly 95/5). The amount of people who have the right combination of raw intellect, disregard for social convention, etc., to make independent and objectively defensible arguments that aren't simple regurgitations of the party line is probably 5%. This is true for basically every group and subculture (possibly except those that are so small they don't qualify as their own group/subculture yet).

Even among groups that attract primarily intelligent people in the absolute sense, like software or physics, most don't have the social courage to speak up when they disagree or to align themselves with someone who is clearly in the minority, nor do they have the interest to consider material in-depth and fully understand it in a way that allows them to internalize its principles and detect fakes or imposters. For the most part, they'll happily follow the crowd, no matter how silly the basis.

From the study:

As a measure of cognitive ability, we used a 10-item vocabulary subtest from the WAIS. In this subtest, participants are presented with a target word and are asked to select the word from a list of five words that comes closest to the meaning of the target word (Cronbach α = 0.67, M = 6.96, SD = 1.90). The participant's score on this test was used as measure of his/her cognitive ability. Although the use of a subscale to measure cognitive ability may be less informative than full-fledged intelligence tests (see De keersmaecker et al., 2017), such tests tapping into a specific aspect of intelligence can be a valid alternative when administration of broad IQ tests are not feasible.

Although I don't think the study mentions "stupid people." And strictly speaking, you're probably not going to be able to administer even the 10-item vocabulary test before deciding how to make a first impression on someone.