As things stand, 65-year-olds get enrolled in Medicare. Buy-in is something of a different beast: Folks between 55 and 64 with access to the exchange could choose to buy Medicare. That sets up an apples-to-apples comparison. And that apples-to-apples comparison is not going to come out well for private insurers, as Medicare has a large and acknowledged price advantage over them. They might be fine with that, because no one wants to insure 60-year-olds anyway. But I doubt they’re going to be fine with a world in which people see the full difference between the prices private insurers offer and the prices a robust public insurer can offer. That, after all, is why they fought the strong public plan so ferociously.