I've noticed this as well. I think it has to do with people self-sorting to different parts of Twitter based on what kind of political discussion they want. The

I've noticed this as well. I think it has to do with people self-sorting to different parts of Twitter based on what kind of political discussion they want. The people who just want to be loudly scornful of $OUTGROUP go to the places where that happens all the time, avoiding the parts of Twitter they'd find boringly calm; and people who'd rather talk about things calmly stick to the places where that's the norm, avoiding the parts of Twitter they'd find to be content-free sound and fury. (And if you ever look at the replies to a tweet that crossed the streams, you get a glimpse of a strange other world.)