When Bill Clinton emerges as an ObamaCare critic and even President Obama admits in a recent interview that his entitlement has “got real problems,” the discipline of the law’s apologists must be fading. The question now is whether Republicans can capitalize to improve U.S. health care from its ObamaCare bottom.

For years liberals have depicted the law as an end-of-history achievement, dismissing genuine problems as partisan inventions. ObamaCare remains as unpopular today as when Democrats rammed it through Congress in 2010,...