Mr. Trump could lose support as delegates become free to vote as they please.

Most states “bind” their delegates to candidates based on primary results. But most delegates are released if no candidate wins a majority in an initial vote at the convention, so those who were bound to Mr. Trump could shift their support. This scenario is less likely if Mr. Trump is close to 1,237 delegates, or if he continues to face a split opposition.

First vote At least 5 percent of delegates are not bound to candidates and can vote as they please from the outset. Needed to win 95% bound to a candidate 5% unbound Did one candidate get a majority of delegates? Yes. That’s it. He’s the nominee. No. Move on to a second vote with some new rules. Second vote After the first round of voting, more than half of all delegates, from more than 30 states, become free. 39% bound to a candidate 61% unbound Did one candidate get a majority of delegates? Yes. That’s it. He’s the nominee. No. Move on to a third vote with some new rules. Third vote Many states with a large number of delegates (like California, with 172) release them before the third vote. 18% bound to a candidate 82% unbound Did one candidate get a majority of delegates? Yes. That’s it. He’s the nominee. No. Move on to a fourth vote with some new rules. This could go on for a while, but it’s very unlikely. It would be difficult to get through more votes without one candidate receiving a majority, because many states release their delegates early if candidates withdraw from the race or do not meet a certain vote threshold on the floor, preventing those with low support from remaining in contention. First vote At least 5 percent of delegates are not bound to candidates and can vote as they please from the outset. Needed to win 95% bound to a candidate 5% unbound Did one candidate get a majority of delegates? Yes. That’s it. He’s the nominee. No. Move on to a second vote with some new rules. Second vote After the first round of voting, more than half of all delegates, from more than 30 states, become free. 39% bound to a candidate 61% unbound Did one candidate get a majority of delegates? Yes. That’s it. He’s the nominee. No. Move on to a third vote with some new rules. Third vote Many states with a large number of delegates (like California, with 172) release them before the third vote. 18% bound to a candidate 82% unbound Did one candidate get a majority of delegates? Yes. That’s it. He’s the nominee. No. Move on to a fourth vote with some new rules. This could go on for a while, but it’s very unlikely. It would be difficult to get through more votes without one candidate receiving a majority, because many states release their delegates early if candidates withdraw from the race or do not meet a certain vote threshold on the floor, preventing those with low support from remaining in contention.

An “eight-state rule” could come into play.

Currently, in addition to securing a majority of delegates, a candidate is required to win more than 50 percent of delegates in at least eight states to secure the nomination. Mr. Trump has already done so in eleven.

However, this rule, or any other, could be changed before the voting begins, putting candidates who do not win a majority in eight states into contention.

The people who are selected as delegates in the first place will be key.

Because delegates are free to vote for their candidate of choice once they are unbound, Mr. Trump and some of the other candidates have already begun organizing their supporters to get as many allied delegates as possible selected.