Michael,
I do not think the democracies of the past would tell us everything we need to know about our own democracy and that is because democracy is not merely a description of a form of government but also at least insofar as the common good is concerned, democracy has a prescriptive connotation. The American argument, (according to Kissinger's work "Diplomacy") for spreading democracy over the world was not a historical one built on the principle of causality and historical description: it was a judgment of value or as R S Peters claims a policy judgment claiming what ought to be the case. The Greek fear of a democracy in which unnecessary desires becomes the obsession of rulers and ruled and the rule of law becomes an arbitrary process was enough to strike fear into the greek heart. I see no reason to believe that the Greek account this is not an acceptable historical account of the democracies of the past(There are many historically accepted documents bearing witness to this fact and the causal processes involved)
Betsy ,
Everything turns upon what one means by a government by the people. I personally doubt whether Trump could be subtle about anything as complicated as this but you are right to draw attention to Brexit and that is surely an issue of sovereignty versus the Kantian project of Cosmopolitanism which the EU venture is all about. Turning one's laws over to other parties has had its negative aspects. The different nuances of French, German and English law can appear exaggerated to those who do not have the patience to wait for the European adventure to mature into a true cosmopolitan project. Aristotle pointed out that if the many can engage judicially in decision-making processes then the resultant decision will usually be less perspectival and more universal. We in Europe(and 48% of Britain) believe in Aristotle and Kant and government by people with as many different interests as possible but these people must know and respect the law. Some Brexiteers have suggested that government by the Eu is beginning to resemble government by a body which is not remaining true to Aristotelian and Kantian Principles and there may be some truth in this. But this situation is not in any way similar to the situation in the US where Republicans and Democrats refuse to accept the principle that the common good is the common ground of both parties.