From Mark Pazniokas:

Lieberman’s endorsement of Republican John McCain disqualifies him as a super-delegate to the Democratic National Convention under what is informally known as the Zell Miller rule, according to Democratic State Chairwoman Nancy DiNardo.

Miller, then a Democratic senator from Georgia, not only endorsed Republican George Bush four years ago, but he delivered a vitriolic attack on Democrat John Kerry at the Republican National Convention.

The Democrats responded with a rule disqualifying any Democrat who crosses the aisle from being a super delegate. Lieberman will not be replaced, DiNardo said.