I left when I was told I had to get behind Kerry, who voted for the Iraq War.
I couldn't do that. I wasn't allowed to have an opinion. I wasn't allowed to say I was voting 3rd party, even when asked the question directly.
At the time I switched over to Huff Po, because it was far more open and although you had to deal with right wing trolls, it wasn't an echo chamber. It was mostly left minded people and so many people who were in the same position I was. Couldn't vote for Kerry, obviously wasn't voting for bush... just wishing for a viable 3rd party candidate. Green party it was.
I stayed on Huff po for a long time until they changed their comment system to use Facebook. I still use it sometimes with a fake FB account.. but most people have gone and you can't have full discussions the way you used to.
If god forbid Clinton becomes the nominee.. then many of us will leave. I never planned on voting for her. I only came back to the democratic party and this website for Bernie Sanders. I registered democratic just to avoid confusion (although I could technically vote as an independent in Cali, I wanted to make sure there was no confusion.) I will be changing my party affiliation on June 8th.
DU will continue on lower numbers, much like DailyKos has done since declaring Clinton the winner. People will go away, but in 2019 when we are picking a candidate to run against Trump, we will find out way back here to support the progressive.