IF ONE IS ASKED to explain why the American government aets as it does with respect to almost any policy issue, the chances are probably eight in ten that the right answer is the separation of powers. The existenee of three separate institutions with independent eonstitutional standing and, in two eases, distinct electoral constituencies is what distinguishes Ameriean government from parliamentary demoeraeies. The separation of powers is the source of the enormous influence that Congress exercises over both the broad outlines and minute details of public policy, an influence that has led Daniel Patrick Moynihan to remark that the United States is the only major government with a legislative branch and that leads many European observers to doubt that this country is really governed at all. The separation of powers is also at the root of the eourts’ authority to deelare presidential and congressional acts unconstitutional and thus is a major cause of one kind of judicial activism.