FTC Chair Lina Khan considers blocking some roll-up strategies on anti-trust grounds

This doesn't seem to make much mathematical sense. If a merger from idk 15% -> 40% market share would be outlawed, then at least one of the mergers to get from 15% -> 25% -> 30% -> 40% (for example) would have to be illegal too. If antitrust law were only based on deltas, Khan's logic might make sense, and the Clayton Act does indeed bar "substantially lessened competition" which might wink at that concept. But the law also outlaws mergers that "tend to create a monopoly" which was logically meant to take care of exactly this kind of problem.

It's crazy for the government to block a 15% -> 25% merger that would be legal alone by speculatively wishcasting that the pro forma entity might make further acquisitions later on. And if you wait to prosecute after several roll-ups, what's the remedy? Do courts have to throw out just the latest merger or also throw out the last two to five roll-ups? How would the legal system even oversee that process if integration was completed over several years rather than operation as a standalone subsidiary? None of this makes much sense.