There is great danger in this view, and it opens the door to abuse by Congress of the power of taxation. If a federal statute purports on its face to be a tax measure, and in fact to some extent operates to that end, the courts cannot ordinarily set it aside, even though the motive for its enactment be to accomplish an object not entrusted to the national government. The jurisdiction of the courts is limited. Legislation which seeks to effect illegitimate ends cannot always be nullified. The power of Congress to levy a graduated inheritance tax as a revenue measure would be practically unlimited unless, in the particular instance, the law were so extravagant, and its unconstitutional object so plain, as to establish beyond doubt an unauthorized purpose. It is not within the province of the judicial power to determine whether a given tax which raises revenue is reasonable or unreasonable, or to inquire into the motives of Congress in enacting the law. The courts might not, therefore, be able to set aside an inheritance tax law passed by Congress even if it absorbed fifty per cent. or more of successions, although it might be quite apparent that the real object of the law was to invade the province of the states and to regulate inheritances in clear violation of the spirit of the Constitution. Nothing could be better calculated ultimately to undermine our whole system of constitutional government than the idea that the courts alone are the guardians of the Constitution and that Congress may rightfully enact any statute which the courts cannot properly nullify. The truth is that the duty of preserving and defending the Constitution in all its integrity is vested in Congress and the President far more than in the courts, and that if Congress and the President do not observe the restraints and limitations imposed by the Constitution, Congress may pass many statutes which are unconstitutional in substance but which the courts cannot set aside. It is often urged that all questions of constitutionality should be left to the courts and not be passed upon by Congress or the President. The true doctrine, however, is that Congress should not enact and the President should not approve any statute which they, as the agents and representatives of the people, are not satisfied seeks to accomplish a legitimate end within the scope of some power delegated to Congress and not reserved to the states or to the people. They should first determine, as their oath of office requires, whether, according to their best judgment, the act is or is not constitutional. It was the distinct intention of the framers of the Constitution, and they so provided in express words, that every member of Congress, every senator and every representative, should be bound by oath or affirmation to support the Constitution, and that the President, especially, should be charged with the duty of preserving, protecting and defending it to the best of his ability. This duty