[antidesitter]

> Isn't the American president a barometer or descriptive reflection of the democratic population?

For a sufficiently loose definition of “reflection”, yes. For a sufficiently tight definition of “reflection”, no.

> does one define American conservatism by reciting a prescription of what people ought be when they say they're conservative

One defines conservatism by a set of values and policies. The same goes for liberalism, fascism, communism, environmentalism, nationalism, etc.