Republicans could change the rules of their convention to permit some kind of preferential ballot. The rule change would have to be proposed in advance, so that members of the convention’s rules committee have time to consider it before voting on it during the week before all the delegates arrive in Cleveland. Then, if it passes the committee, a majority of delegates would have to vote for it too.

When it came time for the delegates to vote on the presidential nomination, delegates would rank their candidates — with pledged delegates putting the candidates to whom they are pledged at the top of their lists. It would probably also be necessary—to reduce the likelihood of accusations of dirty tricks — for each delegate to make his or her rank orderings public immediately after the vote.

It’s a process that would generate a majority for a candidate automatically: There would no need for multiple ballots, and thus no politicking between rounds of voting. The process would also be formally neutral. My guess is that most of the delegates who are not pledged to either Trump or Cruz will prefer the senator to the billionaire, and so the process will work to Cruz’s advantage. But it is certainly possible that Trump would win the instant runoff — and even possible, if less likely, that a third candidate could.