The Socialist Pary did call each other Comrade by the way. Still do as far as I know. And sings the Internationale at the end of the convention. So it's not a slur to call Sanders Comrade. (It just sounds 1930ish which is about where Sander's thinking is on public policy.)
Anyways, here's Comrade Sanders in The Progressive responding to this question,
Q: So what’s your message to progressives?
[Conclusion of Sander's answer] Why is it that two-thirds of white, rural men voted Republican? Why? That’s what we have to address. That’s crazy. These people are working longer and longer hours. They can’t afford to pay $3.50 for a gallon of gas. They’re losing their jobs. So why do they vote for President Bush? And the Republican Party? We’ve got to address this.
It’s very easy to make fun of George Bush, but that ain’t going to do it. What we have to do is knock on doors and go into communities where there are people who disagree with us on certain issues.
And we have to talk to them. They’re our friends. They’re our allies. They’re our co-workers. We can’t see them as enemies.
That’s easier said than done.
All over this country you have progressive communities like Madison and Burlington, but we’ve got to go well, well, well outside of those communities. We’ve got to go to the rural areas. We’ve got to go where a lot of working people are voting Republican.
We just can’t talk to each other. That’s too easy.
The crazy thing is many people vote based on beliefs, principles, and their analysis of politics.
The really crazy thing is not respecting that and having to lecture the progressives to please not consider people who might think liberating Iraq was good for the Iraqi people and American security, that abortion is murder, that same-sex marriage isn't a basic human right, that maybe putting Social Security into a personal account one can pass onto their kids is a good thing; aren't enemies.
There just thoughtful people who don't vote the narrow economic interest Comrade Sanders preceives for them.
The fact Sanders doesn't outline those certain issues is telling. Progressives simply can't talk abou them because they understand many Americans just disagree and they can't persaude them otherwise. They can't layout a progressive case that holds water with voters except in Burlington and Madison. So they're stuck in the hip communities.