Lieberman's unique. There is no other Democrat currently on the hosizon that Republicans would vote for enmasse. Without strong Republican support that third route wouldn't work.
I'm excluding Zell because he retired.
I would never vote for him because I disagree with his social policies, but if he were elected, I would at least feel secure that he was working hard to protect and defend our nation. There aren't many Ds out there who I could say that about.