Separating across what lines? Within group difference might be more severe than between group differences even. Most people identify as independents, there are more than two sides, and even if there were two sides, we're geographically intertwined. Conservatives threaten conservatives and liberals threaten liberals all the time, maybe even moreso! and that's not to mention religious conservatives vs libertarian conservatives, lefists, centrists, etc et. al.
I actually think it’s possible a national divorce makes the problem worse. Lots of these killers have not had clear motives or “sides”