Whoever wins the Democratic primary has a responsiblity to win this damn election. I know that nobody can control that outcome with complete certainty, but I hope both candidates understand that this is their responsibility. Once they win the nomination, they have one job. I don't really think any electability arguments are particularly persuasive. I can see how Bernie Stalin and Hitlery Clinton will both face some problems (people are free to have their opinions on this, I just don't really have one). The point I'm making is...it's your job to win. Make it so.
