One tragedy of the Affordable Care Act is that we already know what its regulations will do to insurance markets, because the states have been conducting policy experiments since the 1990s. But we also know from the states that the damage is reversible, as shown by Maine's emerging insurance turnaround.

In 1993, Augusta passed coverage laws that resemble those that ObamaCare is about to impose nationwide: Insurers could only vary premiums within narrow bands regardless of age or health status, a regulation known as community...