The short answer: a recession.

By one important measure, the economy is doing nicely; the unemployment rate was 3.8 percent in March, close to a 50-year low. But that tends to be a lagging indicator, as employers are reluctant to let workers go until they have no choice. Much other data, related to factors as diverse as housing, borrowing, consumer confidence and manufacturing, hints that the decade-long economic expansion may be in jeopardy.

The stock market was happy to put its faith in the Fed’s renewed commitment to buoy the economy through most of the first quarter; even after losing a bit of ground in the final week or so, the S&P 500 rose 13.1 percent. But bond traders seem unconvinced.

The yield on 10-year Treasury issues sank from about 3.2 percent in October to 2.44 percent on March 22, less than the 2.45 percent rate on three-month Treasury bills. That condition, an inverted yield curve, didn’t last long. The 10-year rate on Thursday was 2.5 percent; the three-month rate, 2.36 percent. But the brief inversion suggested that investors were anticipating slow growth for a long time, dovish Fed or not.

Although the extent of the Fed’s ability to influence the markets is open to debate — the changes it makes to the interest rates it sets tend to follow changes in market rates — Komal Sri-Kumar, president of Sri-Kumar Global Strategies, said the Fed could support the stock market if other factors, such as valuations, cooperated.

“If it’s very overvalued and the Fed cuts rates to help, it’s not going to prevent a correction,” he said.

Mr. Sri-Kumar expects the Fed to reduce interest rates in June and September. Valuations are reasonable enough, in his opinion, that “the Fed has a chance” of propping up stocks, but if it continues to cut after that or begin a new round of asset purchases, even with stocks doing well, it may prove counterproductive.