not to underplay the effects of online manipulation/astroturfing/bots etc, but the fact print media has been in freefall for a while means outrage = clicks = revenue for most news outlets. tv news is no different really. everything is a 'debate' now.
and the left are traditionally way easier to divide because there are so many minorities with diff concerns; the rise of gotcha-ism is super easy to leverage for the right, exaggerating fault lines that have always existed but been kept quiet.
and then add in the fact that every time something outrageous happens on the right, the left media think it's a great idea to never shut up about it, giving it oxygen etc.
yaxu