Since the F.T.C. investigation closed, the complaints against Google have expanded. Competitors that have complained to American regulators include Yelp, the consumer review site, and travel sites like TripAdvisor.
European regulators have accused Google of abusing its dominance in the smartphone industry with its Android operating system, which is used in 80 percent of the world’s smartphones. In July, European regulators fined Google $5.1 billion for automatically installing its search engine and other apps on Android phones.
Sundar Pichai, the company’s chief executive, has rebutted allegations of antitrust violations, as well as the accusations of biased results. After the European decision, he said on Twitter that “rapid innovation, wide choice, and falling prices are classic hallmarks of robust competition.”
“Android has enabled this and created more choice for everyone, not less,” he added.
The reference to “falling prices” points to a hurdle for any investigation. John Sherman, the Ohio senator for whom the Sherman Antitrust Act of 1890 is named, was able to decry monopolistic overcharges as “extortion which makes the people poor.” Modern antitrust theory revolves around the notion that unless there is direct harm to consumers, there is no case. Google’s services are free to consumers, while Amazon has helped drive down prices.
The queasiness over the big tech companies is more spiritual than financial. Polls show a growing anxiety about the influence of technology on American lives, and the issue has emerged as a litmus test for the 2020 Democratic presidential field.
Ms. Warren said that she had been “talking for years about how Google is locking out competition.” A billboard her campaign erected last month near a train stop in San Francisco was meant to appeal to Silicon Valley commuters, particularly those who have been squeezed to distant housing by the area’s tech-fueled property boom.
It asks passers-by to “join our fight” to “Break Up Big Tech” by sending a text message.
On Saturday, a spokesman for Senator Bernie Sanders of Vermont, another leading contender, said the senator “has been trying to sound the alarm for years that the concentration of economic power in the hands of a few threatens our democracy and leads to rigged political and economic systems.”