There are a minimum of 3 delegates per primary race that are NOT chosen by the candidate, but are chosen by the party bosses. That is 171 delegates that may be obligated to vote for a candidate but are NOT obligated to protect that candidates issues on rules changes. Then there are the shenanigans about “at-large” and even district level delegates being “assigned” to vote Trump but not necessarily Trump loyalists for rule changes.
If the establishment doesn’t wake up soon and stop this nonsense of defying the voters, they are going to find themselves the heads of a party with no members. Even if we all unite behind their candidate and beat the immediate threat of Hillary or Bernie or Biden, the exodus will still happen and in 2018 they will lose the House.
Immediately after this election they could be patting themselves on the back right up until the big news story is the formation of a new party and the mass re-registration away from the GOP.
Those aren't "shenanigans" - it is the way delegates are selected. The primary or caucus determines who the delegate is obligated to vote for on the first ballot. But the actual delegates are usually selected at state party conventions weeks after the primary. Some states allow the candidates to submit slates of delegates, but in others, the delegates run for election in precinct, county and state conventions. So a candidate has to have a good organization AFTER the primary to get as many of his supporters selected as delegates as possible. Trump is just discovering this apparently.
Take SC for example - Trump won all 50 delegates. But in order to be selected as a delegate, you had to have attended the state convention in 2015 - months before Trump even jumped into the race. So the likelihood that the Trump delegates in that state will actually be Trump supporters is slim and none.