This November, voters in rural Perry County, Mo., will face a ballot with candidates for a bevy of local offices: state senator, state representative and circuit judge; two county commissioners, sheriff and many more. What they won’t face is a choice. Each of the 17 down-ballot races in Perry County has only one candidate. Just south, Cape Girardeau County fares only slightly better: Three of 12 races have two candidates. All the candidates in the uncontested races are Republicans. And...