In National Review, Ramesh Ponnuru lays out a eminently reasonable explanation of constitutionalism. It’s a newly controversial topic, with a number of factors influencing its relevance: the rise of the Tea Party, the constitutionality of Obamacare, and the debates about federalism in the early going of the GOP primary, among other things. Ponnuru defends the idea of a broadly originalist constitutionalism:
Constitutionalism, in short, is simply a special case of respect for the rule of law: the case in which the law in question is the supreme law of the land. The rule of law demands that those who apply the law — be they judges, sheriffs, presidents, or governors — apply it faithfully. If those officials can change the meaning of the words, there is no point to having a written law.
There are different types of originalism, and legitimate debate about what counts as originalism. But constitutionalism — which is, again, to say the rule of law — entails some sort of originalism. The law has to be knowable, and its meaning has to be fixed at the time of enactment (although, of course, its application may change based on the circumstances to which it applies). Officials who have to interpret the Constitution may or may not err in ascertaining the original meaning of the provisions at issue, or in inferring what norms that meaning implies, or in applying the norms to the legal case or policy dispute at hand. But any authoritative interpretation of the Constitution that departs from plausible understandings of the original meaning is itself a violation of the rule of law. Hence originalism is not merely one interpretive methodology among many.
To put it another way, constitutionalism rules out certain courses of action. It means that it is never acceptable for a congressman to vote for unconstitutional, or even doubtfully constitutional, legislation on the theory that the courts will sort it out. Nor can a constitutionalist judge treat the Constitution as simply raising questions — e.g., what is the right relation of society to the individual? — to which the judge makes up an authoritative answer. Both are cases of disobedience to the Constitution.
Current liberal-conservative debates about constitutionalism are not so much about jurisprudence as they are about whether officials are bound by the rule of law or a fixed rule of law in the first place, with liberals taking the position that they are not.
The next step for Ponnuru: defining Consitutional Conservatism.