On Tuesday, the actress Cynthia Nixon kicked off her primary challenge to New York Democratic Gov. Andrew Cuomo with a campaign stop in Brooklyn. Cuomo has frequently butted heads with the progressive movement in the nation’s second-largest blue state, and in Nixon those progressives have a high-profile champion. But Nixon’s campaign will have to overcome more than just Cuomo—she’ll be playing on a field designed to protect incumbent elected officials. In New York, the deadline to change your party registration to be able to participate in the 2018 Democratic primary was October 13th.