Via NARA [see the full posting here] About the Electors – What are the qualifications to be an Elector? The U.S. Constitution contains very few provisions relating to the qualifications of Electors. Article II, section 1, clause 2 provides that no Senator or Representative, or Person holding an Office of Trust or Profit under the United States, shall be appointed an Elector. As a historical matter, the 14th Amendment provides that state officials who have engaged in insurrection or rebellion against the United States or given aid and comfort to its enemies are disqualified from serving as Electors. This prohibition relates to the post-Civil War era.

Each state’s Certificates of Ascertainment confirms the names of its appointed electors. A state’s certification of its electors is generally sufficient to establish the qualifications of electors.

Who selects the Electors? Choosing each state’s Electors is a two-part process. First, the political parties in each state choose slates of potential Electors sometime before the general election. Second, on Election Day, the voters in each state select their state’s Electors by casting their ballots for President.

The first part of the process is controlled by the political parties in each state and varies from state to state. Generally, the parties either nominate slates of potential Electors at their state party conventions or they chose them by a vote of the party’s central committee. This happens in each state for each party by whatever rules the state party and (sometimes) the national party have for the process. This first part of the process results in each Presidential candidate having their own unique slate of potential Electors.

Political parties often choose Electors for the slate to recognize their service and dedication to that political party. They may be state elected officials, state party leaders, or people in the state who have a personal or political affiliation with their party’s Presidential candidate. (For specific information about how slates of potential Electors are chosen, contact the political parties in each state.)

The second part of the process happens on Election Day. When the voters in each state cast votes for the Presidential candidate of their choice they are voting to select their state’s Electors. The potential Electors’ names may or may not appear on the ballot below the name of the Presidential candidates, depending on election procedures and ballot formats in each state.

The winning Presidential candidate’s slate of potential Electors are appointed as the state’s Electors—except in Nebraska and Maine, which have proportional distribution of the Electors. In Nebraska and Maine, the state winner receives two Electors and the winner of each congressional district (who may be the same as the overall winner or a different candidate) receives one Elector. This system permits the Electors from Nebraska and Maine to be awarded to more than one candidate….”