Let's trace the legislative path of a relatively minor health-care amendment recently adopted by the Congress. The exercise not only illustrates the intricacies and peculiarities of the legislative process but also foreshadows the immense battles to come when — as is now expected soon — the Administration undertakes a serious effort to create a national health-insurance system.But first it might be useful to stress something that is so obvious that it tends to blend unnoticed into the political background: Whatever else medical care in the United States may be — good, bad, wasteful, humanitarian — it is also a . . .