NEW YORK—One year after helping President Donald Trump win the election and earning more than $15 million from a dozen political candidates and committees, the data firm Cambridge Analytica doesn’t have any U.S. political clients, according to an analysis of Federal Election Commission records.

Research firms that work with winning campaigns usually benefit from their victory and the higher profile it brings. President Barack Obama’s data-centric 2008 presidential run spawned numerous digital firms that are still major political vendors.

Yet Cambridge Analytica’s reputation is facing challenges on several fronts. The company has come under scrutiny in congressional investigators’ probe of whether Trump associates colluded with Russia in the 2016 election, according to three people familiar with the firm’s business. The data firm is also grappling with staff upheaval and complaints from clients that it fell short in delivering services it promised, according to several previous clients.

Two groups run by Republican strategist Todd Wilcox that encourage business leaders and veterans to run for office paid Cambridge Analytica more than $150,000 in 2016 for data services. Mr. Wilcox, chairman of Restore American Leadership, said he didn’t get his money’s worth.

“I did not see any indication that they can live up to their claim to be able to use data to change audience behavior,” he said. “My super PAC reverse engineered the process to do internally what Cambridge Analytica offers, at a fraction of the cost.”