A congressional candidate challenged an Illinois rule allowing mail ballots cast by Election Day to be counted if received afterward. The lower courts held that he lacked standing. The Supreme Court reversed. A candidate has a concrete and particularized interest in the rules governing the counting of votes in his election, including the competitive effects of allegedly unlawful ballots and the resources required to respond to those rules. The injury is not merely a generalized interest in lawful government. Because Bost adequately alleged an electoral injury traceable to the challenged policy and redressable by judicial relief, the case was remanded for consideration of the merits.