Lieberman the weak link in the chain?

I have been reading some rumbling on Daily Kos, as well as Talking Points about the possibility of Sen. Lieberman getting on board with the President's plan to reform Social Security. Clearly this would be a quite bad for the Dems. To be successful as an opposition party we need to stay unified to be effective. Allowing the term "bi-partisan" to be attached to this bill would be a massive set back because not only would it weaken the Democratic party's position on the issue but also strengthen the Republicans' resolve. If Social Security is going to be reformed in this way I, as a democrat, would like to be able to point right at the Republican party for the fallout from this very costly change. I told the Sen. that he needs to stand tall with his party right now and i think that every else should too. Sen. Lieberman.