Basically backup to the President.
(Every week someone asks this question) At the start of every month I make a poll asking if and with which party you want to run. You then are put on the party ballot. If you win the party ballot you can advance to the Presidential Ballot. If you win that you are the President. You can promote yourself anytime in that time period.
You can’t choose. The person with the second most votes on the party ballot runs for Vice President.