Each political party nominates long-standing party activists and officeholders for the position of presidential elector. Most nominees for the position of presidential elector are nominated by district and state conventions of political parties, but a variety of other methods are used. For example, in Pennsylvania, the presidential candidate himself or herself directly nominates their presidential electors.
Members of the Electoral College are elected by each state and the District of Columbia on the Tuesday after the first Monday in November in presidential election years -- that is, on Election Day November 3. This date is set by law by Congress, and can only be changed by Congress.
Forty-eight of the 50 states elect their presidential electors using the so-called "winner-take-all" rule -- that is, 100% of the state's presidential electors are awarded to the candidate who received the most popular vote in each separate state.
In Maine and Nebraska, one presidential elector is elected from each of the state's congressional districts, and two presidential electors are elected statewide. For example, in 2016, Maine's electoral votes divided 3-1, with Clinton receiving three and Trump receiving one. Trump received one as a result of Trump's winning one of Maine's two congressional districts.
The 538 members of the Electoral College cast their votes for President and Vice President in meetings held in the 50 state capitals and the District of Columbia in mid-December of presidential election years. In 2020, the designated day for the meeting of the Electoral College is Monday, December 14, 2020.