Building a majority party involves creating coalitions within the party, not circular firing squads. That means we all have to compete cleanly within the party primary, then swallow our pride and support the nominee who was chosen by the majority of our fellow Democrats, who are not really our political opponents, much less enemies.
I was talking about Hackett and Senator Schumer there, but it goes for Lieberman, too. It even goes for anyone who loses to a Democrat to their right. We can't afford to fight each other this year. There is too much at stake!