During the Clinton administration, laws were passed that did a disservice, and thus angered, many who had traditionally supported Democrats. The Clintons ARE supposed moderates, and they are the power brokers of the party. So yes, Democrats have contributed to the dissent.
Think about it.
Unregulated airwaves and political radio...that's propaganda, and people allow the emotional centers of their lizard brain to react, bypassing their logic and reason centers. It's not just for Republicans. Right here on DU, how many posts are there every day, every weekend, about the political talk shows on teevee and how "great" those that say what DUers want to hear are, and how angry do people get at hearing something they don't agree with? Opinions have become sacred, and fighting enemies is a sacred sport. Enough so that people line up on the couch in front of their teevees for political talk like it's the superbowl, to cheer their "side" on and hate the other.
So sacred, in fact, that Democrats can't stand to hear dissent within the ranks, which is why even Democrats here at DU are silenced and tombstoned when they do. Dissent is not looked at as an opportunity for a substantive discussion and evolution of ideas that bring people together, but as something that must be silenced, squashed, and kicked out. The effect of those efforts is to further disenfranchise and anger people, which feeds divisiveness.
It's a national disgrace, imo, and it's not restricted to Republicans or to the political or religious right, although they certainly are a large part of the problem.