The point of our system of government, as prescribed in the Constitution, is that government would not be left SOLELY to the latest class of men and women who fill her seats, but that it would all be limited to a certain set of principles infused into the Constitution.
We do not use the Constitution much anymore, however, since the average joe doesn't care to enforce it. Without strict public oversight, government is an irresistible "gold bar". (Read more about that here if you like: http://www.jackpelham.com/2012/11/18/the-gold-bar-metaphor/)
In short, our system of government has proven to be a failure since the people do not want to oversee their own government and to keep it on the straight and narrow.
But back to your question, being a constitutional republic, and not just a republic, presupposes that men are NOT angels and that they DO need some just laws to govern their behavior in office. What we have proven in this "experiment" of government is not only that men are not angels, but that not enough men care about sound principles enough to insist on them, even when they are already agreed upon and established in the Supreme Law of the Land.
And if that doesn't paint us as a sorry lot, I don't know what does. We are an unprincipled nation that does not even care enough to notice that it breaks its own law.
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