I wouldn't be so quick to call the pro-Sanders bias of /r/politics astroturfing. If /r/politics is truly as left-leaning as you say (I agree), then it is expect

I wouldn't be so quick to call the pro-Sanders bias of /r/politics astroturfing. If /r/politics is truly as left-leaning as you say (I agree), then it is expected that they would prefer Sanders ideologically over Clinton (who, 30 years ago, would be considered a moderate Republican). And that is before issues with her record come into play: the internet is exceptional at revealing politicians' flip-flops and lies. This hurts Clinton, so you'd expect more bias against her. So there is definitely a bias, but remember, this is a community which celebrates 4/20. That they'd oppose a candidate who wants to keep the consumption of marijuana as a felony should not be considered artificial.