Many U.S. households find themselves in a fragile position financially, even in an economy with an unemployment rate near a 50-year low, according to a Federal Reserve survey.

The Fed's 2018 report on the economic well-being of households, published Thursday, indicated “most measures” of well-being and financial resilience “were similar to, or slightly better than, those in 2017.” The slight improvement coincided with a decline in the average unemployment rate to 3.9 percent last year, from 4.3 percent in 2017.

But despite the advance, the results of the 2018 survey indicated that almost 40 percent of Americans would still struggle in the face of a $400 financial emergency. The statistic, which was a bit better than in the 2017 report, has become a favorite rejoinder to U.S. President Donald Trump's boasts about a strong economy among Democratic politicians, including 2020 presidential candidate Kamala Harris, the U.S. senator from California.