Here at ENC.com.  The report states:

“When Mooppan said the lawyer for the Justice Department seemed to argue that Nix could have avoided his injury simply by running as a Democrat or a Republican, Tatel suggested that there might be “constitutional problems” with forcing people to give up their state-created right not to affiliate with a political party they do not want to represent.”

And in a deliciously ironic line, the story notes:

“An official with the U.S. Department of Justice declined comment Monday when contacted by The Free Press.”