Besides these three cases, expressly named in the Constitution, there are two others, where it has already undertaken to exercise _judicial powers_, not by virtue of express words, but in _self-defence_:-- 1. With regard to the conduct of its servants, as of its Printer; 2. When its privileges have been violated, as in the case of William Duane,[17] by a libel, or in the case of Nugent,[18] by obtaining and divulging a treaty while still under seal of secrecy. It will be observed that these two classes of cases are not sustained by any text of the Constitution. If sustained at all, it must be by that principle of universal jurisprudence, and also of natural law, which gives to every body, whether natural or artificial, the right to protect its own existence,--in other words, the great right of self-defence. And I submit that no principle less solid can sustain this exercise of power. It is not enough to say that such a power would be _convenient_, highly convenient, or important. _It must be absolutely essential to the self-preservation of the body_; and even then, in the absence of any law, it must be open in our country to the gravest doubts. “Doubtless,” says Blackstone, “all arbitrary powers, well executed, are _the most convenient_.”[19] But _mere convenience_ is not a proper reason, under a free government, for the assumption of powers not granted; and this is especially the case where the powers are arbitrary and despotic, and touch the liberty of the citizen. Now, if the present inquiry were in the House of Representatives, and were directed against the President or the Secretary of War, on the ground of negligence or malfeasance at an important moment, it would be clearly within the jurisdiction of that body, which has the _sole_ power of impeachment; but it would not come within the jurisdiction of the Senate, until it became the duty of the latter body to try the impeachment instituted by the House. But the present inquiry is neither preliminary to impeachment nor on the trial of an impeachment. It has no such element. It is precisely the same as if an inquiry should be instituted into the murder of Dr. Burdell in New York, or into the burning of slaves in Alabama, or into the banks of New York, or into the conduct of the Supreme Court of Wisconsin in alleged obstructions of the Fugitive Slave Bill,--with regard to all which the Senate has no judicial powers. And yet it has judicial powers in all these cases, precisely to the same extent that it has in the case of John Brown at Harper’s Ferry.