THE APPOINTMENT of Michel Barnier, the European Union’s former chief Brexit negotiator, as France’s new prime minister on September 5th brings to an end two months of political wrangling and procrastination. President Emmanuel Macron announced the decision after a merry-go-round of talks with a succession of figures from across the political spectrum, in an effort to break the impasse generated by an inconclusive parliamentary election result in July. Mr Barnier’s selection closes one tense and heated chapter. But it opens another, which could be even more testing.