I kind of feel sorry for him. It is more evidence that there isn't room for people in the middle anymore.
He isn't in the middle. He's a corporatist boor.
There's a difference between being in the Middle and intentionally going out of your way to alienate people through extreme moderate heroism, especially with regards to the War in Iraq and the Patriot Act. His shenanigans during the Healthcare debate didn't win him any friends on either side of the aisle, and were probably the death knell of his career.
And of course, there's also this:
Something's wrong in America when somebody like Lieberman can be considered a 'centrist' or 'middle-ground' guy.