Alton, Illinois, holds a partisan city election on April 4, 2017. An independent candidate for Mayor, Danny Rauschkolb, filed a petition but that petition has been challenged. No one alleges he lacks enough valid signatures. But the challengers say he can’t run as an independent because he filed a petition to run in the Democratic primary for the same office earlier. That petition was rejected because he didn’t include a receipt showing he had filed a statement of economic interests.
This article explains the details. Illinois voter registration forms do not ask applicants for a choice of party, or whether the applicant is an independent. Therefore the challengers’ reliance on the U.S. Supreme Court opinion Storer v Brown is not fully relevant. Storer v Brown upheld a California law that required independent candidates not to have been registered members of a qualified party, but California had partisan registration.