Who will win the Republican Party nomination for the US presidential election? (update)

Well, this is all getting pretty crazy, isn’t it?

Trump is on track to win enough delegates to win the Republican nomination. He currently has 338 of the 1,247 total needed, and is at 114% of the pace needed to get there, given his particular strengths and weaknesses. Cruz (236 delegates, 61% of the pace) and Rubio (112 delegates, 46% of the pace) are well off the pace[1].

How likely is it that either Cruz or Rubio will get to 1,247 before Trump, given the current state of affairs? Rubio would have to win about two-thirds of all of the remaining delegates to overtake Trump. He’s averaging something closer to 25% of primary voters, which, because of the (semi) proportional nature of the early Republican contests has allowed him to pick up roughly 25% of the delegates. However, the Republicans are about to head into a series of winner-take-all contests. If Rubio can beat Trump and Cruz in many of the winner-take-all states, then he has an outside chance of catching up. But that’s a mighty big “if.” So far, Rubio has beaten both Trump and Cruz in only 1 of 15 (a little more than 6%) states. Rubio would have to move from this pace to one in which he won 20-25 of the remaining 35 states (fudging here because it depends which states he would win), and that sounds highly unlikely to me, even if some of these states are more favorable to Rubio[2]. I doubt that Cruz is in a better place. While he currently has more than twice as many delegates as Rubio, he has failed to win enough southern states (with large numbers of Evangelical voters who tend to be sympathetic with him), and Texas, the state that best combined his advantages with Evangelical voters and has a large numbers of delegates, is now in the rearview mirror[3]. I can’t see how either Rubio or Cruz have much more than a 15% chance of beating Trump to 1,247. So – being as generous as possible to both Cruz and Rubio – it seems like the space of possibilities is carved up in roughly this way:

  • 70% Trump
  • 15% Rubio
  • 15% Cruz

And yet. I think there’s a roughly 20% that there will be a contested convention and Trump will be denied the party nomination. So that means a more accurate assessment of Trump’s chances are as follows: (0.8)*(0.7)+(0.2)(0) = 0.56. What happens if Trump is denied the party nomination after winning enough delegates to qualify? I’m really not sure, but I suspect that there’s about a 40% chance that the nomination will go to Rubio (who appears to have fairly good prospects as a general election candidate), about a 10% chance it will go to Cruz (who has rather poorer prospects as a general election candidate and who’s not at all liked by the party elders), and about a 50% it will go to some sort of compromise candidate – Mitt Romney, John Kasich, Paul Ryan, Anybody But Trump. That means we’re looking at something like this:

  • 56% Trump ((0.8)*(0.7)+(0.2)(0))
  • 20% Rubio ((0.8)*(0.15)+(0.2)(0.4))
  • 14% Cruz ((0.8)*(0.15)+(0.2)(0.1)
  • 10% None of the Above ((0.8)(0)+(0.2)(0.5))

All things considered, this forecast probably underestimates Trump’s chances, but the primary campaign has been so surprising in many ways that I think a little caution is a good idea.

[1] http://projects.fivethirtyeight.com/election-2016/delegate-targets/

[2] http://www.vox.com/a/presidential-primary-delegate-tracker

[3] http://www.vox.com/2016/3/3/11155110/mitt-romney-donald-trump-speech

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