The United States’ 250th birthday carries ambitions to galvanize Americans behind nationwide community-service drives and patriotic brand launches. Well-known U.S. nonprofits hope to inspire a record-setting level of volunteerism, while major companies such as Walmart and Coca-Cola are sponsoring tributes and selling limited-edition merchandise. But the private sector’s unifying ambitions have been met with a mixed response, complicated by an uneasy national mood. Fewer Americans see their count