Though hearty annual growth rates were common for most of the postwar era, the economy has not expanded by 3 percent or more in a full calendar year since 2005 .

Growth figures can swing from one quarter to the next, and the Commerce Department will revise this latest result twice more, as more data comes in.

Other parts of the economy have demonstrated a reassuring sturdiness. Although the number of jobs created each month has drifted down, for instance, the jobless rate is still at its lowest point in decades. And the stock market continues with regular bursts of enthusiasm like the record high the S&P 500 reached Monday.

The trade battle with China is a wild card.

Word from Mr. Trump that the United States and China are close to completing what he calls “Phase 1” of an agreement helped calm some of the roiling anxiety swirling around trade relations. But there have been no substantive details on what a pact would include, and analysts remain wary that this potential breakthrough, like previous ones, could be followed by an abrupt policy reversal from the White House.

“There’s been a big drop in business confidence, across the board,” said Ian Shepherdson, chief economist at Pantheon Macroeconomics. “This ‘Phase 1’ thing is trivial compared to enormous obstacles.”

Summertime shopping might have been given an artificial lift by importers who rushed to bring in goods from China before tariffs were scheduled to increase in September, Mr. Shepherdson added. But that short-term gain, he warned, could mean a falloff in the next three months.

Grady Cope, founder and president of Reata Engineering, a design, tooling and production firm in Englewood, Colo. , offered a guarded outlook.