A slowdown in bank lending is turning into ground zero for a debate over the growing gap between economic hope and reality in the wake of Donald Trump's U.S. election win.

The deceleration in loans made to companies and consumers has befuddled some analysts who worry that the worst growth rate in about six years bodes ill for the U.S. recovery at a time when expectations remain high. With credit acting as the lubricant for economic expansion, solving the mystery of the downturn has gained fresh urgency as investors wait to find out if the enthusiasm tied to Trump's pro-growth agenda will translate into a tangible boost.

“One of the stories for optimism at the start of the year was that the gain in confidence and financial market deregulation would spur a rebound in credit creation,” said Michelle Meyer, an economist at Bank of America Corp. “Surprisingly, the data show the opposite.”