You can find the government’s brief on the merits here. You can find the brief of the Republican Party making similar arguments here. Because the government has taken the unusual position in attacking the constitutionality of a law passed by Congress, the Court appointed an amicus to argue in favor of the law’s constitutionality. The Democratic Party also intervened to defend the law. Their briefs will be filed later.

The Republican Party brief cites a blog post by Rick Pildes and Bob Bauer, The Supreme Court, the Political Parties, and the SuperPACs, ELECTION LAW BLOG (June 24, 2025).