In mid-March, President Joe Biden nominated a young scholar named Lina Khan to serve on the Federal Trade Commission. Khan is a progressive’s progressive. Frustrated at what she viewed as Amazon’s anti-competitive practices, she argued as a 27-year-old Yale Law student that the “consumer welfare” standard — that antitrust action should only be pursued when business practices are adversely affecting consumers, not competitors — was inadequate for dealing with the company’s growing dominance. She suggested that one way to address this problem would be to force Amazon to split up retail and marketplace operations. Another possible solution floated involved more hands-on regulation, as if Amazon were a kind of public utility. Liberals loved it. Khan advised Massachusetts Democratic Sen. Elizabeth Warren and a Democratic FTC commissioner, then took a job as a counsel for Rhode Island Democratic Rep. David Cicilline’s antitrust subcommittee. The old guard on the Right was less entranced by Khan’s ideas. Joshua Wright, a former FTC commissioner and current scholar at George Mason University, which serves as a home base for classical conservative economic thinking, denounced Khan’s camp as “hipster antitrust.” Then-Utah Republican Sen. Orrin Hatch said this new school of antitrust thought “amounts to little more than pseudo-economic demagoguery and anti-corporate paranoia.” Yet when Khan’s nomination came to a vote, something genuinely surprising happened: Khan sailed through the Senate with 72 votes. Twenty-one Republicans, or about 40% of the GOP caucus,...