84. The executive power of the United States is vested in a President. The executive is single,—that is, one person. He possesses all the executive powers which the sovereign,—the people of the United States, have conferred. His power is derivative, not original. His power is not defined by the Constitution, that is, it is not fully set forth by limitations. It is limited in two particulars: he cannot grant reprieves or pardons in cases of impeachment, and he solemnly swears or affirms faithfully to execute the office of President of the United States. This solemn obligation implies that he himself is not the sole or the final judge of his fidelity in executing his office. This responsibility of the President to a superior, in certain cases, is clearly stated by the Constitution itself: first, that the House of Representatives shall have the sole power of impeachment, and secondly, that the Senate shall have the sole power to try all impeachments, and when sitting for that purpose, its members shall be on oath or affirmation. When the President is tried, the Chief Justice of the United States shall preside, and no person shall be convicted without the concurrence of two thirds of the members present.[220] 85. Whether or not the President has performed the duties of his office is a political question and may alone be determined by impeachment and conviction. President Johnson was impeached but not convicted,—whence the conclusion that he faithfully executed the office of President. The term “office” is not used in the Constitution as descriptive of the exercise of legislative power by either House or by its respective members. Senators and Representatives receive a compensation for their “services.” No person holding any “office” under the United States can be a member of either House during his continuance in “office.”[221] But the Constitution does not apply the term “office” to the two-year term of a Representative, or to the six-year term of a Senator, or to the duties, rights, privileges, qualifications, or powers of either. We shall see that the term is applied to judges of the United States.