How Microsoft’s Legal Legacy Shapes the Antitrust Case Against Google

Antitrust trials are full of long stretches of detailed, often tedious testimony punctuated by telling moments. In the two-month Google antitrust trial that is nearing its conclusion, one of those moments came in a brief exchange in October.

While cross-examining a witness for the Justice Department, John Schmidtlein, Google’s lead trial lawyer, tried to describe how this suit differed from the landmark antitrust case brought against Microsoft in the 1990s. The barriers to competition in search today, Mr. Schmidtlein said, are less daunting than Microsoft’s stranglehold on personal computer software.

The judge cut him off. “Let’s move on,” said Judge Amit P. Mehta, who wrote in an opinion earlier in the year that he would use the Microsoft case as a guiding framework. “I think I can figure out what the Microsoft case was about.”

The antitrust fight against Microsoft in the 1990s has loomed over the government’s showdown with Google. The Justice Department and a group of states say the search giant is running the Microsoft monopoly playbook, just in a different tech market, while Google argues that it is hardly as powerful as Microsoft was back in the day.

The Microsoft antitrust case is also the lone example of the government’s embarking on — and winning — a sweeping suit against a tech giant for illegally protecting its monopoly. Microsoft combined old-style practices, like bullying industry partners to stifle competition, with newer ideas in economics.

One of those new ideas included the dynamics of digital markets, which reinforce the power of a dominant company. In tech markets, there can be a powerful “network effect” as a product or service becomes more valuable as more people use it, attracting still more users and investment. Once on a digital platform, users tend not to switch. These concepts of digital platform economics are crucial to the Google case.

While the eventual ruling by Judge Mehta, who was appointed by President Barack Obama, will hinge largely on his assessment of the facts and evidence presented in the trial, his decision must also be built on the precedents established by previous cases.

“Microsoft is his legal road map,” said Andrew I. Gavil, an antitrust expert and law professor at Howard University.

Testimony in the trial, which began in September, is expected to end by Thanksgiving. A ruling by the judge…