This morning another takeover among America’s five big health insurers was announced: Anthem, the second-biggest, is buying fifth-ranked Cigna for $48 billion. Earlier this month Aetna agreed to purchase Humana for $37 billion. One prompt for the wave of mergers is the Supreme Court’s approval in June of the subsidies for health insurance as laid down in the Affordable Care Act (or Obamacare): these have created a larger, lower-margin industry. Another is that insurers want extra clout in bargaining with drugmakers and hospital groups, which are also bulking up. But the deals create headaches for two lots of people. First, America’s antitrust watchdogs: they must consider whether three (or even four) insurers are too few for consumers’ good. And second, bosses at UnitedHealth, the biggest of the five, which will face heftier and more formidable rivals—unless it can upset one of the deals.