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The Department of Justice's (DOJ) antitrust probe into Google is honing in on the company's third-party advertising business and its impact on and influence over publishers and advertisers, according to The Wall Street Journal.

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Investigators are reportedly looking into two potentially anticompetitive decisions: Google's integration of its ad server, a tool for publishers selling ad space, and its ad exchange, the industry's largest ad marketplace; and second, Google's decision to require advertisers to use its tools to buy ad space on YouTube following its acquisition.

The news follows a recent evidence-sharing meeting between the DOJ and state attorneys general, who issued a subpoena questioning Google's ad products last fall.

The development could signal that investigators are closing in on a particular topic (Google's third-party advertising) to build an antitrust case around. In line with such a decision, the DOJ's chief antitrust investigator recused himself from the investigation last week due to his involvement with the FTC's approval of Google's acquisition of the DoubleClick ad server in 2007.

The news also follows multiple rounds of interviews between investigators and publishers like New York Times Co., Gannett, Condé Nast, and News Corp., likely looking to understand whether Google has abused its position as the industry middleman to the detriment of these publishers. The search giant appears to be preparing for the worst on this front: The Journal reports that Google execs have had informal conversations about preemptively divesting their third-party ad tech business.

With greater clarity into the plans of antitrust regulators, we can speculate about the likelihood of a few (not mutually exclusive) outcomes for Google.

High confidence: Google will invest more heavily in AdWords and Search advertising — its first-party ad business — relative to its third-party operations. And even if the investigation does not force divestment from or other significant changes to its third-party business, we expect Google will still prioritize its search product due to industry trends — like the dissolution of third-party cookies.

Moderate confidence: Google will offer more favorable terms to publishers and digital advertisers, reducing its influence as the middleman between the two. And based on the Journal's report, investigators are likely making a case for some kind of structural change to how ads are bought and sold through Google's ad platform.

Low confidence: Regulators will force Google to divest entirely from business segments like YouTube, Maps, or other G-suite products. These business segments have not received the same attention from regulators as its other ad products, likely because it's hard to prove that their development or acquisition has had an anti-competitive effect. In other words, making a legal argument that YouTube was a direct rival to Google Search at the time of acquisition is a tall order, and investigators likely haven't discovered anything in the ballpark of Facebook CEO Mark Zuckerberg's emails directly characterizing WhatsApp as a Facebook competitor at the time of purchase.

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