“Companies are starting to do what they do when there is rampant uncertainty, which is just stop issuing guidance,” said Savita Subramanian, head of United States equity strategy at Bank of America Merrill Lynch. “Companies just basically go dark.”

During the three months that ended in September, companies in the S&P 500 offered the fewest updates — positive or negative — to investors since 2000 , according to the bank’s analysts.

The “rampant uncertainty” that Ms. Subramanian referred to flows from many sources: signs that the economy and job growth are slowing, evidence that the manufacturing sector may already be in a recession, and the trade war’s toll on China, Japan and Germany.

Plus, politics and the 2020 presidential election were always going to be a distraction, but the impeachment investigation has made it harder to know where policy will go.

On Friday, President Trump said the United States and China had reached an interim deal to avert a planned tariff increase on Tuesday. But the agreement was spoken and would take several weeks to write, doing little to remove the uncertainty surrounding the economic battle between Beijing and Washington.