Where does the Constitution say anything about Presidential elections?
The Twelfth Amendment (Amendment XII) to the United States Constitution provides the procedure for electing the president and vice president. It replaced the procedure provided in Article II, Section 1, Clause 3, by which the Electoral College originally functioned. The amendment was proposed by the Congress on December 9, 1803, and was ratified by the requisite three-fourths of state legislatures on June 15, 1804. The new rules took effect for the 1804 presidential election and have governed all subsequent presidential elections.
Under the original rules of the Constitution, each member of the Electoral College cast two electoral votes, with no distinction made between electoral votes for president and electoral votes for vice president. The presidential candidate receiving the greatest number of votes—provided that number equaled a majority of the electors—was elected president, while the presidential candidate receiving the second-most votes was elected vice president. In cases where no individual won a vote from a majority of the electors, as well as in cases where multiple individuals won votes from a majority of electors but tied each other for the most votes, the House of Representatives would hold a contingent election to select the president. In cases where multiple candidates tied for the second-most votes, the Senate would hold a contingent election to select the vice president. The first four presidential elections were conducted under these rules.
The experiences of the 1796 and 1800 presidential elections – showing that the original system caused the election of a President and Vice-President who were political opponents of each other, constantly acting at cross-purposes – spurred legislators to amend the presidential election process, requiring each member of the Electoral College to cast one electoral vote for president and one electoral vote for vice president. Under the new rules, a contingent election is still held by the House of Representatives if no candidate wins a presidential electoral vote from a majority of the electors, but there is no longer any possibility of multiple candidates winning presidential electoral votes from a majority of electors. The Twelfth Amendment also lowered the number of candidates eligible to be selected by the House in a presidential contingent election from five to three, established that the Senate would hold a contingent election for vice president if no candidate won a majority of the vice presidential electoral vote, and provided that no individual constitutionally ineligible to the office of president would be eligible to serve as vice president.