WASHINGTON — U.S. consumer confidence tumbled this month to its lowest reading in a year and a half, tested by the partial government shutdown and roiling financial markets. Still, consumer spirits remain robust by historic standards.

The Conference Board, a business research group, said Tuesday that its consumer confidence index fell to 120.2 in January, down from 126.6 in December and the lowest level since July 2017.

The index measures consumers' assessment of current economic conditions and their expectations for the next six months. Both declined in January. Consumers' expectations for the future dropped to the lowest point since October 2016.

The government reopened Monday after the 35-day shutdown, the longest federal closure in U.S. history. The shutdown is expected to cause slight permanent harm to the economy — about $3 billion — according to a new government report.

The January decline in consumer confidence "is more the result of a temporary shock than a precursor to a significant slowdown in the coming months," said Lynn Franco, the Conference Board's senior director of economic indicators. He noted that "shock events" such as government shutdowns "tend to have sharp, but temporary, impacts on consumer confidence."

The U.S. economy is healthy. Economic growth clocked in at a brisk 3.4 percent annual pace from July through September after surging 4.2 percent in the second quarter. At 3.9 percent, the unemployment rate is near its lowest level in five decades. And the U.S. stock market is steadier after its wild gyrations and heavy losses late last year.