Obamacare allowed young adults to stay on their parents’ plans until they turn 26. It’s a wildly popular feature and a successful one. The uninsured rate for 18- to 25-year-olds has dropped by more than 50 percent since 2010 — a steeper decline than for any other age group. Taking away this provision of the law – even though it might help stabilize the broader health system — is politically toxic to both Democrats and Republicans because it would antagonize millions of middle-class voters.

The under 26 provision has contributed to one of Obamacare’s biggest flaws: Not enough young, healthy people have signed up for coverage in the law’s insurance marketplaces, or exchanges.

That’s translated into financial losses for insurers, big premium spikes and dwindling competition. Those are the problems that Republicans repeatedly cite when they argue that Obamacare is collapsing, and therefore they have no choice but to take drastic action to salvage the health care system.