President Trump promised an economic golden age when he returned to office last year. Instead, voters are in their crankiest mood in years about their financial outlook — and the pessimism is spreading even to Republicans. Why it matters: The growing GOP gloom could hardly come at a worse time for Trump and the party — less than six months out from a midterm election that's likely to turn on the economy. The big picture: Trump's approval rating has been dropping for months, but the University of Michigan's May consumer sentiment survey released Friday revealed something more striking: Republicans are beginning to lose confidence in the economy, too. Republican and independent voters' attitudes about the economy hit a low point of Trump's second term, per the survey. Overall sentiment hit an all-time low, period. Expectations that inflation will remain high shot up among everyone surveyed — but especially Republicans.…