The current Republican presidential campaign has not only been full of surprises, but it has led to a situation with such a maelstrom of unpredictable factors that the range of possible scenarios for the Republican's nominating convention in July is extraordinarily wide.
Here's a lay-out of the apparent possibilities:
1) Trump wins on the first ballot. Likelihood: 40%. (Likehoods here calculated from the political futures markets, where people who think they know something place bets on outcomes, and whose collective wisdom generally is superior to individual judgments.)
That scenario would likely produce the least chaotic convention. Although much of the Party regards a Trump nomination as a recipe for a disaster in the fall, and other Republicans running this year would likely try to separate themselves from the top of the ticket, a first-ballot Trump nomination seems least likely to produce disturbances on the convention floor or on the streets outside.
2) Trump is nominated on a subsequent ballot. (Likelihood 10%.)
3) Cruz gets the nomination on a later ballot. (Likelihood: 34%)
Those who want to avoid a Trump nomination are hoping for a "contested" convention. But the stop-Trump forces also face the threat of outrage from Trump and his backers if the candidate with the most support from the base is denied the nomination. There are dangers of upheaval within the convention and perhaps even ruptures in the Party afterwards.
But the futures markets are saying that if he survives the first ballot, Cruz has a better than 50-50 chance of being the nominee.
4) Someone other than Trump or Cruz emerges as the nominee. Likelihood 16%.
A lot of the support now for Cruz is not really for him but is backing Cruz only as a way of stopping Trump. Cruz also poses problems for the Party: he is reportedly almost universally disliked by those who know him, and many fear that his ideological extremism would make him only a little less disastrous to have at the top of the ticket than Trump.
Putting anyone else's name into nomination would require the Party to change its rules. The rules from 2012 were designed to block Ron Paul from disrupting Romney's convention, and by those rules only Trump and Cruz will meet the criterion for being put into nomination.
The rules committee, which meets in the week prior to the convention, can adopt whatever rules it wants. But as Trump and Cruz share an interest in confining the options to the two of them, how likely is it that a majority of delegates on that committee will act contrary to the desires of both leading candidates?