A quiet but consequential directive has reached the antitrust division of the US Department of Justice: pause the cooperative work it has long conducted alongside Canadian competition authorities. The two nations have for decades built a shared architecture of enforcement — coordinating investigations, aligning priorities, and exchanging the kind of sensitive information that major cross-border cases require. Whether this pause reflects a momentary recalibration or a deeper reorientation of how the United States engages its closest trading partner on matters of market power remains, for now, u