Senate Republicans are struggling to agree on health reform, and the biggest divide concerns Medicaid. The problem is that too many seem to accept the liberal line that reform inevitably means kicking Americans off government coverage.

This narrative serves the liberal goal of scaring the public to preserve ObamaCare, but center-right and even liberal states have spent more than a decade improving a program originally meant for poor women and children and the disabled. Even as ObamaCare changed Medicaid and exploded enrollment,...