On August 11, attorneys for the state of South Dakota filed a brief in Libertarian Party of South Dakota v Krebs, 4:15-cv-4111. The lawsuit was filed by the Libertarian and Constitution Parties on June 15, 2015, against the March petition deadline for a newly-qualifying party. The state’s brief says the Libertarian and Constitution Parties haven’t been injured by the deadline (so far, at least) and therefore they don’t have standing.
Three times, the U.S. Supreme Court has found that minor party or independent candidates do have standing to challenge restrictive ballot access laws whether they have tried to petition or not. Many lower courts have issued similar opinions, including the Eighth Circuit itself. South Dakota is in the Eighth Circuit. The South Dakota government brief does not mention any election law cases, just cases involving standing in other areas of law.