The most harmful TV show in American history
This rift is between those I would call "nice liberals" and those I deem "fighting liberals." The main thing that distinguishes them is that nice liberals have conflated morality with politics, while fighting liberals better understand that politics is a power play, not a war of virtues. Nice liberals have watched too much West Wing, and think that our system's institutions will somehow save us because they are manned by good people with our interests at heart. Fighting liberals are more likely to identify with Veep, with all that implies. Nice liberals are more interested in maintaining institutions and norms, fighting liberals are more interested in winning. This division also has little to do with Bernie versus Hillary. Though Sanders had a social democratic message, the vast majority of his supporters, like Clinton's, were liberals.
My realization of the nice versus fighting rift came while attending many protests this year. At the those I've been to, the vast majority of attendees have been liberals, not leftists. However, they are most definitely of the fighting variety. The first protest I went to was organized by labor unions to call to protect health care, all the way back in January. It was a liberal crowd, but of fighters. Cory Booker and Robert Menendez even got raked over the coals for failing to support a bill to lower drug prices.
If you want a clear distinction between nice liberals and fighting liberals, just look at the response today to Jeff Flake's speech. The nice liberals were falling over themselves to give praise. This speech is catnip to their West Wing sensibilities. They want to believe that there is some kind of basic decency shared on both sides of the aisle. Fighting liberals responded differently. They tended to point out that Flake still votes for Trump's agenda, and that his dropping out of his Senate race was more a reflection of his unwillingness to face a primary challenge than anything else.
If the Democrats are to be successful going forward, they need more of the fighting spirit and less of the "nice." That nice was "when they go low, we go high." That nice was expecting the Trump campaign to collapse on its own accord. The fighting spirit has been awakened since last November, it needs to be the dominant mindset among liberals if they are going to have any hope for change.