Yes, at least one dyed-in-the-wool Democratic operative is now attached to this scandal. And yes, at this late date the only realistic alternative is that the seat goes to a member of the other party. I would hate to be a Republican partisan in Alabama right now, and if I were I'm genuinely not sure how I would choose to vote. That's different, though, than refusing to consider the allegations because they're politically inconvenient. It's possible Roy Moore is a creep. It's also possible half a dozen unrelated people are lying. There's no reason to think those must be equally possible, and there's certainly no reason not to think that one can't make an educated guess as to which is true.

To shift political gears somewhat, our legislature is currently engaged in a debate about tax reform. One party claims the currently proposed plan will cut taxes on the middle class. The other party claims that the plan will raise taxes on the middle class. That's a question of fact, and both positions can't simultaneously be correct. The thought process you engaged in above can be applied equally well to that situation regardless of which party one favors, but it's guaranteed to make at least one party's fans wrong.

When we, as a polity, begin to completely disregard information because it comes from a partisan source or has strong partisan implications then I worry that we lose the idea of a shared reality. We can't convince those who disagree with us, nor allow ourselves to be convinced, if we refuse on general principle to listen to and engage with people who disagree with us.