If Trump does not get a majority of delegates on the first ballot, the rules make his hunt for a majority even more difficult on the second ballot. At that point, nearly three-quarters of the delegates—more than 1,800 of the 2,472—become instantly unbound. They are free agents who can vote for any nominated candidate, with no obligation to Trump even if he won their particular state. The national convention has no authority to amend these binding rules because they are set by each state, and the deadline for states to change their rules has passed.
On the third and subsequent ballots, things would get really unpredictable. Not only would even more delegates become unbound; the current rules also do not require the candidate with the smallest number of votes to drop out, meaning the deadlock can last for endless ballots until a remaining candidate bends.
At that point, a convention can have a mind of its own. The delegations will be a hotbed of rumors, deals and rumored deals. The absolute nightmare scenario is a convention so fractured with so many false rumors spread so quickly and repeatedly—all the more so thanks to social media—that no consensus can be reached. That’s a multi-ballot convention that stretches days beyond the scheduled adjournment.
It is only in this remotest of all scenarios that someone who is not currently a candidate could burst onto the scene. The convention rules committee won’t vote on the criteria for throwing a new candidate’s name into the nomination contest until the convention is actually under way. The committee also has yet to determine whether it can reconvene during the convention in order to loosen the criteria for an outsider to put his or her name up for nomination.