When delegates "pledge" to a certain candidate (after the 1st obligatory ballot), do they sign some kind of binding contract? What keeps delegates from changing their minds and unpledging themselves once they get to the convention?
However, he might still be subject to some kind of discipline -- as in Rubio delegates might choose to do Rubio's bidding. Or Georgia delegates might be enlisted to follow the state party's lead.
In an earlier day, these secondary control points exhibited firm control -- giving failed candidates and state party leaders considerable negotiating power. But I don't think there is much of that left anymore..