A string of disappointing economic data capped by last week's jobs report is prompting even some of the more optimistic economists to question the durability of the U.S. recovery.

While analysts such as Stephen Stanley of Pierpoint Securities LLC and Michael Feroli of JPMorgan Chase & Co. still see growth strengthening in the months ahead, they voiced concern that the lull in the economy may prove prolonged, leaving it more vulnerable to external shocks or policy missteps.

"We'll do better in the second half," said Feroli, chief U.S. economist for JPMorgan in New York and a former member of the Federal Reserve's forecasting team. "That said, the concern is that there's enough weakness that could feed on itself."