WHAT IS THE biggest problem facing America? Or Japan? Or Britain? Or France? Opinions vary, naturally, but some worries crop up again and again. Those of a materialist bent point to decades of slow growth in median incomes, which has bred disillusion and anger among working people. Fiscal hawks decry huge public debts, destined to grow even vaster as ageing populations rack up ever bigger bills for health care and pensions. Then there is immigration, which has prompted a furious populist backlash in the United States and all over Europe. That hints at what, for many, is the most alarming trend of all: the lack of any semblance of a political consensus about how to handle these swelling crises.