From NBC's Luke Russert
Here's a clip from an interview Joe Lieberman (I-CT) did with "The Connecticut Post" newspaper in September of 2009. He flat out says that he supports a Medicare buy-in for those in their 50's and strengthening public options that already work.

Now, Lieberman is 100% against the Medicare buy-in for those 55 and older. This would seem to suggest that Liberman has flip-flopped on the issue outright. His support comes at about 1:04 into the video. (Hat tip: Greg Sargeant at the Plum Line).

Here's the response from Lieberman's office:

Senator Lieberman has long been concerned about making health care more affordable, especially for those over the age of 55 and not yet eligible for Medicare. One idea that has been discussed for years is expanding Medicare to people younger than 65. Senator Lieberman's comment reported by the Connecticut Post in September was made before the Finance Committee reported out the Baucus Bill, which contained extensive health insurance reforms, including a more narrow age rating for pricing health insurance premiums and extensive affordability credits that would benefit this specific group of individuals.

These health insurance reforms and affordability credits have been strengthened in Senator Reid's Patient Protection and Affordable Care Act and will provide even greater relief for those 55-65 years old. Any inclusion of a Medicare buy-in for that same age group would be duplicative of what is already in the bill, would put the government on the hook for billions of additional dollars, and would potentially threaten the solvency of Medicare, which is already in a perilous state. The Senator also has concerns that this provision would result in cost-shifting that would drive up premiums for others, including those with employer-based coverage.