I haven't said anything about Ned Lamont's primary campaign to unseat Joe Lieberman in Connecticut, mostly because, although Lieberman is capable of being a pain, his voting record is mostly solid. Add to that the fact that the issue that steams most other Democrats is his support of the Iraq war, something that can't be undone now. Third, the elevation of Ned Lamont to the U.S. Senate would only succeed in replacing one Democrat with another one, albeit a more progressive one. I think our energies would be better directed at electing Democrats where Republicans currently serve, not in replacing other Democrats.
Having said that, I acknowledge that Lieberman is troublesome to many wanting to build a Democratic majority because he has a disturbing nack of stiffing the party at particularly volatile times and on high profile issues, while playing up his moralizing, maverick status in the media (something that other maverick Democrats, like Nebraska's Ben Nelson, tend to avoid). Lieberman is moreover, the worst kind of moralist: the kind seemingly more obsessed with private sexual matters and provocative language in the entertainment industry than about the morals of war and economics.
And while mavericks and moralizers can be useful to a political party, especially in states where the party is weak, they aren't really necessary in states in which the party's presidential standard-bearer typically wins by double-digit margins, as has been the case in Connecticut the last few election cycles. Hence, Lieberman's problem. For Democrats he's a party contrarian from a state that doesn't need one.