Will Trump have the 1,237 delegates by convention time that are needed to win the Republican presidential nomination? I suspect that he will, but he probably will not win them all in the primaries. If he is somewhat short of the necessary delegates as the convention approaches, he can get them through horse trading. While it is against the rules to pay delegates money for their votes (although that wouldn’t stop some politicians), there is nothing to stop him from trading favors for delegate votes. There are a number of delegates going to the convention who are not bound to vote for a specific candidate even on the first ballot.
At its crudest, Donald Trump could invite some unbound delegates to fly to a weekend retreat in the Bahamas aboard the Trump airplane. A more politically acceptable way of buying votes would be to offer plum jobs to people who control delegates. For example, he could offer John Kaisch or Marco Rubio or even Ted Cruz a prime cabinet position in exchange for instructing their delegates to vote for Trump. I hope that John Kaisch is ethical enough not to sell out in that way, but Marco Rubio and Ted Cruz have both demonstrated that they are ethically challenged.
By hook or by crook, I have a feeling that Donald Trump will be the Republican nominee and that he will be nominated on the first ballot. If he is not nominated, the convention will go into a free-for-all. Most delegates are free to vote for whomever they want after the first ballot, and even more are released after the second ballot. We really don’t know which candidate most of those delegates would favor if they were free to vote as they wished, but I suspect they would not vote for Trump.