A campaign for the European Union to become a “United States of Europe” will be the “best weapon against the Euroskeptics”, one of Brussels’ most senior officials has said. Viviane Reding, vice president of the European Commission and the longest serving Brussels commissioner, has called for “a true political union” to be put on the agenda for EU elections this spring. “We need to build a United States of Europe with the Commission as government and two chambers—the European Parliament and a ‘Senate’ of Member States,” she said. Mrs. Reding’s vision, which is shared by many in the European institutions,...