American Exceptionalism is not an abstract concept, but a definable set of ideas and circumstances.
The belief in the inalienable rights of man, endowed by the Creator (and hence off-limits to the revocation by man).
The adoption of a frontier mindset, favoring self-reliance, property rights, self-governance and individual responsibility over reliance on a public safety net. That mindset drove our early development as a nation and attracted the individuals who helped to build it. A desire to embrace that set of opportunities and risks rather than the status quo was the process of selection that formed our unique community and fed its traditions.
Reliance upon the idea that individuals will work harder, defend more fiercely and tend more lovingly, that which they have the freedom to own and make prosper.
A regular supply of ambitious, creative, entrepreneurial risk-takers, from every corner of the globe, who have constantly refreshed the engine of freedom and prosperity that is the American Experiment.
Those ideas, and the results they have produced, are balanced against the fact that collectivism/socialism/progressivism has not, does not, and will not ever work as a large scale system of human organization. It is a parasitic opportunist that cannot develop independently and exists only as long as it can continue to feed off the capitalistic host it is destroying, or manages to enslave it's participants to force their participation.
We have yet to see an example of National Socialism that is able to produce enough to both feed and defend itself independently. Every case where it has been attempted has either already failed or is in varying states of decay and deprivation.
This question is at the core of the conservative debate precisely because we are living through the results of misguided central planning, social engineering experiments run amok, forced scarcity driven by politicized science and an entitlement culture that runs from Wall Street to the inner-city.
Conservatives believe that governance, wealth and freedom should reside with the individual precisely because it is so much more difficult to persuade someone to relinquish any of them for the wrong reasons. Liberals/Progressives are constantly frustrated that it is so difficult to get control of those three elements in order to "try to make things better", despite the evidence that all previous similar attempts have failed.
These ideas lend themselves to endless extrapolation without contradiction because they are so patently correct. Rather than requiring endless exception and circular explanation, they are a font of clarity. They are simple and easily adapted to a lifetime of good governance without need for indoctrination.
All other pursuits of higher learning are foundational, but liberalism is a teetering construct without a clear basis for development of any of its conclusions from a defined set of principles. Its adherents have little appetite for debate or examination and little use for free speech. Their patchwork of beliefs must be repeated, back and forth, continually, to be sustained in the presence of so much objective fact that refutes their validity. It is a set of beliefs in search of a defining truth.
There is no deeper question to be answered in our time, than how long we will subject ourselves as a species, to a set of ideas that has clearly failed.