Francis Lieber explains when and why the judiciary is a fit institution for the assessment of constitutionality

“The supremacy of the law requires that where enacted constitutions form the fundamental law, there be some authority which can pronounce whether the legislature itself has or has not transgressed it in the passing of some law, or whether a specific law conflicts with the superior law, the constitution.   If a separate body of men were established to pronounce upon the constitutionality of a law, nothing would be gained.   It would be as much the creature of the constitution as the legislature, and might err as much as the latter.  Quis custodet custodes?  Tribunes or ephori?  They are as apt to transgress their powers as other mortals.

 “But there exists a body of men in all well-organized polities, who, in the regular course of business assigned to them, must decide upon clashing interests, and do so exclusively by the force of reason, according to law, without the power of armies, the weight of patronage or imposing pomp, and who, moreover, do not decide upon principles in the abstract, but upon practical cases which involve them—the middle-men between the pure philosophers and the pure men of government.   These are the judges—courts of law.

“When laws conflict in actual cases, they must decide which is the superior law, and which must yield; and as we have seen that according to our principles, every officer remains answerable for what he officially does, a citizen, believing that the law he enforces is incompatible with the superior law, the constitution, simply sues the officer before the proper court as having unlawfully aggrieved him in the particular case.  The court, bound to do justice to every one, is bound also to decide this case as a simple case of conflicting laws.  The court does not decide directly upon the doings of the legislature.  It simply decides, for the case in hand, whether there actually are conflicting laws, and if so, which is the higher law that demands obedience, when both may not be obeyed at the same time.  As, however, this decision becomes the leading decision for all future cases of the same import, until indeed proper and legitimate authority should reverse it, the question of constitutionality is virtually decided, and it is decided in a natural, easy, legitimate and safe manner, according to the principle of the supremacy of the law and the independence of justice.  It is one of the most interesting and important evolutions of the government of law, and one of the greatest protections of the citizen.  It may well be called a very jewel of Anglican liberty, one of the best fruits of our political civilization.”