Election security

Presidential Elections: Vacancies in MajorPartyCandidacies and the Position ofPresident-Elect

What would happen in 2016 if a candidate for President or Vice President were to die or leave the ticket any time between the national party conventions and the November 8 election day? What would happen if this occurred during presidential transition, either between election day and the December 19, 2016, meeting of the electoral college; or between December 19 and the inauguration of the President and Vice President on January 20, 2017?
Procedures to fill these vacancies differ depending on when they occur. During the Election Campaign—Between the National Party Nominating Conventions and the Election. After the conventions, which are usually held in July or August, and election day, November 8 in 2016, political party rules apply. For the Democrats, the Democratic National Committee would select a replacement; for the Republicans, the Republican National Committee would select replacement, or it could reconvene the national convention to perform this task.
Between the Election and the Electoral College Meeting. On election day, voters choose members of the electoral college, which formally selects the President- and Vice President-elect several weeks later (December 19 in 2016). Although the transition has begun, party rules still apply: a replacement candidate would be chosen by the national committees of either party, or by a reassembled Republican National Convention.
Between the Electoral College Meeting and Inauguration. The balance of scholarly opinion holds that the President- and Vice President-elect are chosen once the electoral votes are cast. The electoral votes are counted and declared by a joint session of Congress, held January 6 of the year following the election, although Congress occasionally sets a different date for the joint session.