At what point does great wealth held in a few hands actually harm
democracy, threatening to turn a democratic republic into an oligarchy?

That was Latin America for the past 50 years if you look at its history. It is the same situation for many other third world nations. Their main problem, in my view, was the lack of a strong constitution to protect democracy and equality.

What do you mean the signers didn't send other peoples kids to war? We have more or less spent our entire history as a nation at war even before the Constitution existed..

* Revolutionary War
* War of 1812
* Mexican American War
* Civil War
* Spanish American War
* World War I
* World War II
* Korean War
* Vietnam War
* Desert Storm
* Enduring Freedom
* Iraqi Freedom

Not to mention the countless military actions and helping out other nations with their wars/issues.

They did not send their sons IN their place. That is what he meant.