With a lot of input from the civilian "political leadership."
A small group of senior officers meet informally to decide who will get a third star.
With a lot of input from the civilian "political leadership."
Bingo!
Petraeus may influence the selections of one-stars, but it may not be enough, especially if Clinton gets in.
I don't know Petraeus' plans, but it seems he should be given a Unified Command next (obvious play for a second 4-star tour, EUCOM should be open next year), followed by the Chairmanship of the Joint Chiefs of Staff.