The GOP must narrow the Democratic health-care advantage. Too many people are too ready to believe that whatever Democrats offer on that front is better for the country. The GOP’s message for 2020 should emphasize the party’s strengths: taxes, jobs, regulatory relief, defense, energy and judges. But winning will also require Republicans to improve on health care. Unless Republicans make their case confidently and forcefully, the health-care issue could cost them victory in 2020.