The latest Republican plans for replacing Obamacare are focused on financially separating patients with high health care costs from all the rest. If a separate source of funding can be found for the expensive enrollees, competition for the healthier ones will keep premiums more in line with free market pricing. The vehicles are risk pools, “invisible” risk pools and reinsurance. In the latter two cases, the enrollees are generally unaware of the arrangement.

Before Obamacare, 35 states had risk pools—available to people in the individual market who had been turned down for private insurance because of a health condition. For several years prior to the exchanges, there was also an “Obamacare” risk pool, funded by the federal government.