The constitutional powers of the president are stated in the article II, section 1 and section 2. For me the most important role that the president have is that he shall nominate, and by the advice and with the advice and consent of the Senate shall appoint judges of the supreme court. The constitution names other functionaries too, but for me the American system of justice is better than many in the world because all the judges in the supreme court have been good in general terms. For me a good justice system is essential for democracy.