A powerful new litigant has joined one of the most momentous cases slated to be heard by the Supreme Court this term. The respondents in the case of Moore v. Harper filed a brief today that included a surprising new signatory: J. Michael Luttig, who has been known for years as perhaps the most conservative Republican judge in the country. Now, though, he has joined a coalition of veteran lawyers and nonpartisan government-watchdog groups who are fighting against a far-right Republican election-law challenge—one so radical that critics say it has the potential to end American democracy as we know it.

The former judge is a surprising co-counsel to Neal Katyal, the well-known Supreme Court litigator. Katyal is a counsel of record in the case for several respondents, including Common Cause and the North Carolina League of Conservation Voters, that are opposing the far-right groups. The case is scheduled to be heard by the Court on December 7th. Luttig told me that he signed on as Katyal’s co-counsel because he regards Moore v. Harper as “without question the most significant case in the history of our nation for American democracy.” Putting it more colloquially, he said, “Legally, it’s the whole ballgame.”

Having such a well-known conservative former jurist argue against the election-law challenge may carry some weight with the conservative super-majority on the Court, several of whom have ties to Luttig that stretch back decades. Justice Clarence Thomas, for instance, was personally shepherded through his contentious Supreme Court confirmation hearings by Luttig in 1991. At the time, Luttig served as the Assistant Attorney General in charge of the Office of Legal Counsel in George H. W. Bush’s Justice Department. After Thomas was confirmed, Luttig himself was sworn in to a seat on the U.S. Court of Appeals for the Fourth Circuit