1. Of the Senate of the United States. 9.-1. The constitution of the United States, art. 1, Sec. 3, provides that the senate shall have the sole power to try all impeachments. When sitting for that purpose, the senate shall be on oath or affirmation. When the president of the United States is tried, the chief justice shall preside and no person shall be convicted without the concurrence of two-thirds of the members present. See also constitution.