UPDATE May 26th 2016

Moments ago, Donald Trump’s delegate count effectively went above the number needed to guarantee the nomination at this summer’s Republican National Convention.

As reported by NBC, “Donald Trump now has the support of 1,238 delegates — just a hair above the 1,237 threshold needed to clinch the Republican presidential nomination”

UPDATED

The update includes adding actual delegate counts for races so far, recognizing that for Pennsylvania this means only 17 delegates out of 54, even though he won there, because Pennsylvania is strange. Also, some other revisions.

This estimate still uses a combination of polling data and information in this discussion at FiveThirtyEight by Nate Silver, as well as polling data.

My NEW estimate puts him at 1228 delegates, or 9 delegates short. Here’s the data:

Throughout the primary season, Trump has not played the ground game, and Cruz has. That’s why I picked the “Trump shooting himself in the head” picture for the top of the post.

From the original post:

Here’s what I mean by that. Say a state awards 10 pledged delegates to you, and 12 to your opponent. Your opponent. Your opponent is a really great guy, I mean, really great, everybody loves him, and he knows, really knows, how to close a deal. So he figures he’s closed the deal and moves on to the next primary. But you, being a more experienced politician with a ground game, start making calls. You got a 10-12 split, and that will be reflected at the convention when this state casts the first ballot, but after that, the delegates at the convention will be to some degree able to change their vote on the next ballot. So you make these calls, and make sure that all of your own supporters show up at the right time and place to position themselves as national convention delegates. So when the national convention happens, you have 18 people who like you and your opponent has only 4. That does not matter for the first ballot, but it give you a win in that state for the second and beyond ballots.

It is not quite that simple, and the lack of simplicity makes your ground game stronger. There are rules that vary somewhat across states that say that only some of the delegates are free to choose on the second ballot. There are also unpledged delegates from most states, and they vary in number and they vary in how much influence you may have over them. So you expend your resources efficiently to maximally bring delegates, both pledged and unpledged, into your fold. At the end of the day, you win the nomination. And maybe your name is Ted.

I don’t think anybody outside the campaigns has a good idea of what might happen on the second ballot. Even within the campaigns there has to to be a lot of uncertainty. It will be an interesting convention!

A bit of discussion on this on the Rachel Maddow Show: