When Republicans failed to repeal ObamaCare last year, it recalled the old line about snatching defeat from the jaws of victory. That loss, however, should not be allowed to overshadow an important Republican success on health care. Millions of Medicare beneficiaries now get their coverage through private plans under Medicare Advantage—a quiet step forward that brings real benefits. To ensure continued progress, Republicans must resist the temptation to choose short-term savings over long-term reform.