The most common way in which political bias affects research is by influencing definitions and what questions people ask. If you don't think this is real, I suggest you read the discussion in the thread below this. https://twitter.com/phl43/status/1247648567029882881

It's really fascinating because when you read this, it's absolutely clear that he doesn't even realize he's biased. His framework seems totally natural and value-free to him, when it's absolutely clear that it's neither.

The problem is not that he is consciously biased, I don't believe that, it's that he doesn't even realize how his ideology is shaping his research in a fundamental way. It's obvious that, were social psychology more ideologically diverse, this would never have been the case.