Sen. Mike Lee led a grilling Tuesday of a Google official about whether the corporate tech giant has become an illegal monopoly. But unlike others on a subcommittee that he chairs, Lee asserted that proof of possible antitrust violations is the way he says Google mistreats conservatives.

“Isn’t this behavior evidence of market power?” he asked. “In other words, why would any company want to treat its customers that way unless it was confident that its customers had no viable alternative?”

Lee, chair of a Senate Judiciary subcommittee on antitrust, especially complained that Google stopped allowing digital ads sold through it to be placed on the website of The Federalist, a conservative web magazine, denying it income. He said only a monopolist would dare that to try to force a website to change its operations.

Donald Harrison, who oversees corporate development, said the problem was that a reader comment section operated by The Federalist allows people to post “highly racist comments,” and Google does not allow the ads it sells to show up next to harmful content.

He said Google tried to work with The Federalist to solve the problem either by moderating comments, putting a firewall around the commentary section so ads could not appear there or by eliminating the comment section entirely.

Lee complained that such dictating of terms to the Federalist was “ironic, some would say hypocritical” because Google itself has argued that it should not be held accountable for content uploaded by third parties — but seemed to hold The Federalist accountable for possibly racist comments posted by readers.

Harrison responded that Google simply is trying to stop ads it sells from appearing next to objectionable material. He added that Google itself and products such as its YouTube have developed systems that automatically capture 99.8% of such problematic comments before they are posted.

Still, Lee said, “Isn’t the fact that Google acts this way evidence that it perhaps doesn’t feel competition — doesn’t feel threatened even potentially by any competition?”

Harrison said Google has many competitors — and said The Federalist itself even uses 30 digital ad selling tools beyond those offered by Google, although the company has the largest share of available advertisers.

Meanwhile, others focused on such things as Google merging and obtaining many digital ad competitors, such as DoubleClick and AdMob, to help make it the dominant player in online advertising. Google maintains a dominant grasp over each of the many steps between an advertiser looking to place an ad and a website looking to host it.

Sen. Richard Blumenthal, D-Conn., complained, for example, “In no other markets does the same party represent the seller, the buyer, name the rules and conduct the auction. I think that is the nub of the issue here from an antitrust standpoint and seems unacceptable in a really free market.”

Sen. Amy Klobuchar, the ranking Democrat on the subcommittee, complained that Google has at least 80% of the market shares in representing both advertisers and publishers on digital ads. “In the opinion of some experts, Google gained these dominant market share positions through acquisitions” of competitors.

The hearing came after the House more than a month ago held its own exhaustive hearing on potential monopoly power with the chief executives of Google, Facebook, Amazon and Apple.

It also comes after Lee has waged a series of attacks against Google, Facebook and Twitter for what he says are biases against conservatives, despite denials by the tech giants.