An open mayoral election in 2017. This would occur if de Blasio, feeling the heat, either steps down before reelection or finishes out his term but chooses not to run for a second term. In this scenario, the same cast of characters we'd see in a special election would vie for the mayoralty. But the odds of an outside candidate winning would sharply decline — because this would be a partisan election with party primaries, meaning the winner of the Democratic primary would have an inside track to win the general election, as de Blasio did in 2013.