[Macha]

Politicians are generally an older crowd. Obama got a lot of credit in 2008 for twitter use, wherein that use was basically tweeting campaign statements and updates.

It was probably 2016 by the time that politicians realised they could use social media to whip up such strong feelings to maybe benefit their campaigns.

People certainly disagreed with each other online in 2012 (I remember reddit had subreddits dedicated to complaining about how much pro Ron Paul content was posted in the mainstream subreddits), but I think it's the active engagement of the politicians themselves that turbo charged this.