If you can, it would require breaking up the groups and exposing the former members to a different culture. People will gravitate to the bubbles they're most comfortable with. When there's no one there to call out your bullshit you can keep drifting off into more and more absurd territory. One extremist surrounded by opposition will tend to be less aggressive. Knowing no one's going to agree with something will make them less likely to say it. If they don't dislike the people they're surrounded by, they'll try not to offend them. On a scale the size of what we have, I don't think all the damage will be undone. If Trump wins, some of the opposition will be forced to reexamine how their behavior helped lead to Trump's victory, others will only be further radicalized and driven to self-isolation or terrorism. If Trump loses, they won't be driven to do any self analysis, but they may feel relieved and not as threatened, becoming a bit more relaxed and less aggressive. Some will want to continue subduing their opposition, others will be in favor of being more understanding with their friends and family they disagree with. To see those they disagree with as anything less than evil or under the influence of evil, they'll have to be shown that they're severely wrong on some issues they feel strongly about. To feel less threatened, they'll either have to see their opposition subdued, or to see them exorcise restraint and generosity when they're on equal terms or in a superior position.