The Civil War, end of slavery, and making former slaves into full US citizens. I named three. Many of the Founding Fathers foresaw these things but they were not able to address them without compromise. If the northern states had insisted on what they saw as inevitable, the Union would not exist.
The US Constitution was created to replace a very weak government originally founded under the Articles of Confederation. When eleven states decided that they wished to return to that weaker form of government, the rest of the Union resisted and forcibly returned those states to the Union despite what you read in the 10th Amendment.
We are where we are and going back doesn't seem to be an option unless you would choose to sacrifice the Union of our country. So where we go from here seems to be a function of what kind of People are We and where do we want to go. This is the will of the people and it is as fickle as any other kind of popularity.
I hope you are enjoying the discussion as much as I am.
I will list another agency I like:
Bureau of the Public Debt
http://www.publicdebt.treas.gov/