The original Constitution gave presidential electors two votes, not one, and provided that they could only vote for one nominee from their own state. The idea was that electors would use one vote to flatter a local favorite and the other to select a national leader like, say, George Washington, giving him a strong majority.
But alas, the two-vote system could be sabotaged. Electors could simply vote for their favorite Joe Schmoe and cast a blank second ballot, thereby maximizing Schmoe’s chance for success. Enter the vice presidency, a consolation prize for favorite sons (or whoever polled second in the electoral college). It was meant to assure the election of a proper president; providing a replacement executive was a distinctly secondary objective.