"The founding of the American nation was the hinge of world history"

Well, I believe that an argument can be made in that regard. There had been no Republic on earth since the Roman Republic collapsed into tyranny 1800 years before. There was no blueprint for a functioning democratic government extant, and the continuance of the experiment was often in doubt, not often more so than in early July 1863.
Most of us who post here are living in countries in which representative Democracy is such an established paradigm that we no longer think of it as anything special, nor perhaps anything worth protecting. It is, however, what the idea of the United States of America was all about. Whether we currently conduct ourselves in a manner worthy of that idea and that heritage is well worth examining, but I believe that nothing can impeach the nobility of that idea, nor its impact on humanity.