The Clayton Antitrust Act, which dates to 1914, bans mergers that may “substantially lessen” competition or “tend to create a monopoly.” It makes no distinction between vertical mergers and horizontal ones, in which a company buys a rival, thereby reducing the number of competitors in an industry. But in large part thanks to Mr. Bork’s analysis, horizontal mergers continue to receive intense scrutiny from the federal government, while most vertical mergers go forward, albeit often with conditions.

From the publication of “The Antitrust Paradox” through 2016, the government has challenged only 52 of the thousands of vertical mergers, and many of those challenges were focused on horizontal aspects of the deals. None of those cases went to trial. Most were resolved through consent decrees, including Comcast’s 2009 bid for NBCUniversal, which went forward after Comcast and the government agreed to a long list of restrictions on the combined company’s behavior.

The Justice Department last rewrote its vertical merger guidelines in 1984. (The horizontal guidelines have been revised three times since then.) The department largely embraced Mr. Bork’s logic.

But over the ensuing decades, more antitrust experts have questioned Mr. Bork’s laissez-faire approach to vertical merger enforcement, especially in cases involving media and intellectual property.

The most immediate impacts of the ruling on Tuesday are the removal of an obstacle to a megamerger and the likely bursting of a dam of mergers that were waiting the decision.

But the most important aspect of Judge Leon’s opinion is that it essentially embraces the Bork approach, which rested on a few premises: that markets are inherently competitive; that a firm’s dominance in one market cannot be leveraged into another; and that market success is a result of maximizing consumer welfare, not anti-competitive behavior. The theory is that vertical mergers produce efficiencies that can be passed on to consumers in the form of lower prices, higher quality or both.

Not surprisingly, AT&T argued in court that it had no incentive to withhold Time Warner’s programming from other distributors, that consumers would derive many benefits from the merger and that the combined companies would be in a better position to compete with upstarts like Amazon and Netflix, which already are vertically integrated.