No doubt, your observation also applies to the world outside of politics too. Many artists get leeway because their behavior and failings are hoped to be independent (and sometimes a pre-requisite) of their art. And the rationalization we make may have little to do with absolute standards and principles, and more with proximity to the subject and the controversy. For example, I have no problem ignoring/boycotting Roman Polanski's contemporary work while I had a much harder time not caring about Woody Allen's continued work, at least until I read Dylan Farrow's essay about the abuse she faced [0]. It wasn't because that the weight of Polanski being officially charged with rape was more significant than the public evidence against Allen. I just hadn't grown up watching Polanski, where Allen's past movies have been among my favorite. With familiarity and sentimentality, it becomes easier to delay passing judgment, or to have doubts.

In the case of Moore, many of his implicit supporters may not love him. But if their priorities are a conservative and pro-life agenda, it will likely seem rational to them to de-prioritize taking a real look at the accusations against him. Nevermind that for Christians, it's practically tradition that the "work of God" is often carried out by the corrupt and the flawed (e.g. much of the Old Testament).

[0] https://kristof.blogs.nytimes.com/2014/02/01/an-open-letter-...