Auto workers may be getting some extra time off around Independence Day, but they won’t be celebrating. They’ll know it means sales are weak and that profits — and profit-sharing checks — could be shrinking.

Manufacturers used to shut plants for a week or two in July for maintenance and to keep inventories in check. As sales boomed in recent years, most factories cranked out cars without a break. This summer, widespread closures may be back, and for weeks longer than before. The reason: four straight months of declining sales and little expectation the trend will reverse anytime soon.

It’s probably not what President Donald Trump wants to hear. He has admonished Ford Motor Co., General Motors Co. and Toyota Motor Corp. for building factories in Mexico and demanded more U.S. jobs be created, taking credit for some new investments in the U.S. that had been long in the planning.

“You