Biden’s New Antitrust Cop Threatens to Slam Brakes on Mergers

To understand how the Justice Department’s new antitrust chief, Jonathan Kanter, is thinking about his job, take a look around his office.

On one wall hangs a painting of the prosecutor who brought the case that crushed John D. Rockefeller’s Standard Oil monopoly. There’s also a picture of a bison with the words “Ass Kicking Is On My Mind.” And then there are the historic posters from an earlier trustbusting era.

Kanter, an affable 48-year-old with oversized dark-rimmed glasses, is planning an aggressively activist approach to his new job. His mission: to reverse decades of lax enforcement …