The Constitution speaks of the "advice and consent" of the senate, but in practice all the senate does is to give its consent. In the early days, however, the President not infrequently requested the "advice" of the senate before starting the negotiation of a treaty, and if the advice was unfavorable the proposed negotiations were abandoned. Even now if the President has doubts as to whether a proposed treaty would receive the approval of two thirds of the senate he will sometimes consult with the members of the senate committee on foreign relations and with other influential members, before beginning the negotiations. The senate may reject a treaty _in toto_, and has done so in many instances, or it may amend a treaty laid before it, in which case it must be sent back to the government of the other country which is a party thereto for concurrence in the amendments. After the senate has consented to the ratification of a treaty, the President may ratify it or not as he likes. [Illustration: LIBRARY OF CONGRESS, WASHINGTON, D.C.] [Illustration: THE WHITE HOUSE,--THE PRESIDENT'S HOME AND OFFICE] _The Senate as a Court of Impeachment._--Another special function of the senate is that of acting as a court for the trial of impeachment cases. The Constitution declares that the President, Vice President, and all civil officers of the United States shall be removed from office on impeachment for and conviction of treason, bribery, or other high crimes and misdemeanors. Military and naval officers are tried by court-martial and are not therefore liable to impeachment.[29] To impeach an officer is to bring charges against him. So far as federal officers are concerned this power belongs exclusively to the house of representatives, which acts somewhat as a grand jury does in finding indictments against ordinary criminals. When sitting as a court of impeachment the senators are under a special oath, and when the President is on trial the chief justice of the Supreme Court is the presiding officer instead of the Vice President, who, in such a case, would be directly interested in the outcome of the trial, since in the event of the conviction and removal of the President he would succeed to the office. Managers appointed by the house of representatives appear at the bar of the senate to prosecute the charges preferred by the house, witnesses are examined, evidence presented, and the accused is defended by counsel of his own choosing. In order to prevent the employment of the impeachment power for party purposes, the Constitution provides that the concurrence of two thirds of the senators shall be necessary to convict. [29] That members of Congress are not liable to impeachment was determined in the case of William Blount, a senator from Tennessee in 1797, the senate deciding that it had no jurisdiction of the case.