Interstingly, he's suing them for keeping him from competing fairly for the presidency in 2004:
The lawsuit also alleges that the Democratic National Committee conspired to force Nader off the ballot in several states.
"The Democratic Party is going after anyone who presents a credible challenge to their monopoly over their perceived voters," Nader said in a statement. "This lawsuit was filed to help advance a free and open electoral process for all candidates and voters. Candidate rights and voter rights nourish each other for more voices, choices, and a more open and competitive democracy."
Among other things, the lawsuit alleges that the DNC tried to bankrupt Nader's campaign by suing to keep him off the ballot in 18 states. It also suggests the DNC sent Kerry supporters to crash a Nader petition drive in Portland, Ore., in June 2004, preventing him from collecting enough signatures to get on the ballot...
"This is a case designed to make sure other independent and third party candidates will not be subject to the same kind of conspiracy in the future," Afran said.
I wonder if there's any particular third-party candidate whose viability Nader is trying to protect for the future.