On the first ballot at the convention, just over 85% of the 2,472 delegates will be bound to vote for the candidate to whom they are individually pledged. Some delegates are pledged for more than one ballot, but not most. Just under 15% of the delegates – 165 of the 168 RNC committee members – are “superdelegates.” Yes, we have them too – though far fewer than the Democrats. Around 7% of the RNC convention floor will be made up of superdelegates – i.e. people who are automatically delegates separate from the election process. The Democrats will have 717 of them – about 15% of their 4,678 total delegate count. In addition, there will be around 180 delegates from a handful of state and territories that send their delegates “unbound” and who go to the convention as free agents.
After that first ballot, most of the delegates will likewise be free to vote for whomever they choose. Now before you start thinking that Trump, Rubio, Cruz or Ohio Gov. John Kasich would “control” their delegates, understand that this is likely not the case.
Just over 10% of the states have party rules that provide for candidates to choose their own actual delegates – 259 delegates, to be precise (and 169 of those are from one state, California).
However the vast majority (close to 90%) of the delegates are actually chosen through internal party elections of one sort or another. Some are chosen at conventions, some at caucuses. In some states individuals run for delegate, by name, on the ballot. These folks are then “bound” to a candidate, as I outlined above.
Presumably candidate-chosen delegates will have a much higher likelihood of being loyal to their candidate and also more likely to let their candidate “broker” or “throw” their votes as part of a negotiated deal. But again, that’s a small percentage of the total delegate pool.