Hillary Clinton is wrong when she says that Medicare for all is not achievable. In fact, if she and her husband had embraced the concept in 1993, we would be nearly there today.
Medicare was supposed to be a first step toward Medicare for all. After activists tried and failed to include universal health care in the Social Security Act of 1935, and after President Harry Truman tried during his presidency to achieve that goal, supporters decided that an incremental approach was most likely to bring ultimate success.
So activists decided to fight to cover seniors, as a first step. They achieved that goal with the enactment of Medicare in 1965. In 1972, Medicare was expanded to cover people with disabilities. But that is where progress stopped.