J Marshall Presnell
With the terrible polarization that Trump seems to have evoked in the left (and some in the right), I believe that the more extreme left sees this as an opportunity to lurch the country to the far left. They see this polarization and assume that it's a population-wide polarization, while it is predominantly a left wing phenomena.
So, they think (incorrectly) that people will vote for 'anyone but Trump', and it's the perfect timing to put a hard leftist in the white house.
What I believe will actually happen (and it's beginning to happen now): The more rational democrats will see this as a split in the left wing, and oppose the extreme left (internally at first, publicly as time passes), therefore creating a wide schism within the party itself. Over time, the only option they will have will be to disassociate themselves from the extreme left to maintain ANY power whatsoever.
The problem is that the extreme left will see the split (correctly this time) as an attempt to marginalize them. They will then call on their supporters to use any means necessary to remove key democrats from key decision making positions, causing the rational democrats to fight a war on two opposing fronts (the right and the extreme left).
As the extreme left persists (and they WILL persist), their attacks will marginalize some of the rational democrats out of office, further reducing their power base.
The ONLY option for the rational democrats will be to utterly politically destroy the extremists. They can live with the right, but they can't live with the extremists because (and this is important) the extremists choose NOT to live with the rational democrats. It will be an all-out war between the extreme left and the rational left.
The resultant situation will be the end of the rational democrats. They don't know how to fight this type of internal political enemy.
This is a VERY bad situation for us all. We NEED both the rational right AND the rational left in our country. The worst possible situation would be to have an unchecked party in perpetual power. (In case you missed it, history shows that is a very very VERY bad idea!)
Those in the middle and on the right need to come to the aid of the rational left and unite to politically eliminate the extremists that threaten our country's democrat party. You may not like their policies, but they keep the country balanced.