Tens of thousands of protesters marched through French cities on Thursday, heeding the rallying cry of trade unions demanding action against plans for sharp spending cuts in next year's budget. Trade unions are eager to keep the pressure on President Emmanuel Macron and his new prime minister, Sebastien Lecornu, who is racing against the parliamentary timetable to break an impasse in budget negotiations with political rivals. Macron and his prime minister, who is still working to form a cabinet, need to bring public finances under control in the euro zone's second-largest economy, with European Union peers, ratings agencies and financial markets watching its next moves. But union leaders, including those from France's largest union, the CFDT, and the hardline CGT,...