It could roil Silicon Valley, lead to years of bitter court battles, and upend the business model of one of the country's most successful companies. Yet the rationale for embarking on this project is far from clear.
From the start, the government's public explanations have varied widely. Attorney General William Barr said in June that he was concerned about the suppression of conservative viewpoints online. Other officials have mused about biased search-engine results or dominant advertising technology. Trump himself justified the probe because tech companies "discriminate against me."
In the end, the government focused its case on the agreements that Google has signed with phone makers and wireless carriers to promote its search business. On the face of it, the case is questionable: All the relevant agreements were the result of competitive bidding, users face only the slightest of hurdles if they wish to switch to other services, and even the world's most ardent Bing enthusiasts must admit that Google has made a great product with immense consumer benefits.