"A former Racine alderman, Becker was elected mayor of the state's fifth-largest city in 2003. He ran unopposed in 2007 for the nonpartisan office and was elected to a second four-year term."
How does that work ?
Most local offices in Wisconsin are officially non-partisan. They have a single primary and the top two vote getters run in the general election.
It serves to make sure that dems always win in liberal areas.