Taking the Constitution seriously is not a trivial exercise. Randy Barnett is one of the best sources for insight and orientation concerning fundamental issues of US law and the constitution.
Apart from the constitutionality of Obamacare, Randy Barnett covers a whole range of interesting issues in the below interview. Of particular note I find his contention toward the end of the video that the abolitionists were the precursors of modern libertarians.
See also The Classical Conception of Natural Law.