That assumes nobody walks in the door with enough committed delegates to win on the first ballot.
That won't happen. The system is designed against that. It's FAR more likely in the Democrats with Super Delegates.
If the GOP establishment candidates remain to the end, it is not likely Trump will reach the number of delegates needed.
Graham, Kasich, Christie, Rubio may carry their delegates to attempt to give Bush a chance to secure the nomination.
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