Democratic U.S. Senate primary rivals Graham Platner and Gov. Janet Mills are running starkly different campaigns, with the front-running newcomer spending heavily on ads and digital content while the governor pulls back on ads while keeping a big staff. Campaign finance reports released this week show Platner’s team making more than two dozen combined media, digital advertising and video production purchases during the first half the year. Advertising and outreach has made up nearly three-quarters of his spending to date, while Mills has put more than a quarter of her haul into staffing and consultants. The divergent campaign styles put...