Makan Delrahim, Justice Department assistant attorney general for the antitrust division, said there are “very valid concerns at some level” about whether companies in Silicon Valley are getting too big. (Al Drago/Bloomberg News)

The Justice Department’s top antitrust enforcer is receptive to complaints that tech companies such as Google and Facebook may be hindering competition with their dominance but believes regulators lack the economic evidence that would be needed to prove such a case in court.

Makan Delrahim, the agency’s antitrust chief, said Friday at an event hosted by Axios that there are “very valid concerns at some level” about whether companies in Silicon Valley are getting too big, or “stifling innovation or consumer choice.”

In principle, those complaints could ultimately lead to an antitrust suit, Delrahim said. And there is little question that some tech firms enjoy market power in certain markets, he conceded. But Delrahim quickly added that the allegations against the companies thus far are merely “anecdotal stories.”

“I don’t know if any of the enforcement bodies necessarily have that credible evidence,” Delrahim said.

Delrahim’s remarks underscore the shifting regulatory risks for tech companies in Washington. From Congress to the White House, the rhetoric is growing for policymakers to rein in the industry — but few can agree on how, or which government powers should be brought to bear.

Delrahim on Friday also dipped his toe into a swirling debate over whether tech companies' products may be discriminating against conservative viewpoints.

“I’m concerned about the concerns that have been raised,” Delrahim said, “because not so much is it ‘because conservatives,’ but because one day, depending on ownership, it could be liberals. I think you have to be very careful about the power of big companies in a democracy.”

Earlier this month, the Justice Department cited those allegations to justify holding a meeting with state attorneys general to discuss the tech platforms.

Attorney General Jeff Sessions sought to raise the issue of bias several times during the meeting. But state law enforcement officials steered the conversation instead toward the companies' privacy practices and their use of consumer data — indicating that Silicon Valley could soon face greater scrutiny from multiple states over the business model that has created billionaires out of tech executives such as Facebook’s Mark Zuckerberg.

Still, antitrust regulators seeking to penalize the industry would be required to persuade court officials using economic data. And antitrust experts say the problem is that harms to innovation can be difficult to prove. Regulators may never be certain, for example, whether Instagram would have grown to become equally successful had it not been purchased by Facebook.

“We cannot quantify edge innovation, let alone connect it empirically to a platform’s discriminatory conduct,” said Hal Singer, an economist at George Washington University’s Institute for Public Policy. Delrahim, he said, is seeking “an evidentiary standard that cannot be satisfied here.”