The United States Constitution, sent to the states for ratification in 1787, establishes procedures for seating the national legislative and executive branches of the United States Government. Article 1, Section 2 provides for the direct election of Representatives to the House. Article 1 Section 3 originally provided that U.S. Senators be selected by individual state legislatures. Amendment 17 Section 2 (ratified 1913) superseded Article 1 Section 3 and provides for the election of Senators by the people.
Article 2 Section 1 dictated the selection of the President of the United States by chosen electors from each of the states:
The executive Power shall be vested in a President of the United States of America. He shall hold his Office during the Term of four Years, and, together with the Vice-President chosen for the same Term, be elected, as follows:
Each State shall appoint, in such Manner as the Legislature thereof may direct, a Number of Electors, equal to the whole Number of Senators and Representatives to which the State may be entitled in the Congress: but no Senator or Representative, or Person holding an Office of Trust or Profit under the United States, shall be appointed an Elector.