This week in the Republican nomination race, Ted Cruz’s win in Wisconsin triggered buzz about how front-runner Donald Trump might be in trouble. Doubtless today’s win in Colorado will intensify the chatter, and will involve words like “momentum.” It is best to ignore all of that coverage – at least until some national polling data shows a sustained change. Why? Because states differ from one another, mostly in demographics but also in rules and various local factors. It is almost impossible to learn something new from a single race. To know where the race stands as a whole, it is necessary to consider all states at once.
In several ways, Wisconsin was typical. With a pre-election poll median of 36.0 ± 1.5% (median ± estimated SEM), Trump’s vote share of 35% was on the mark, continuing his close match between polls and outcomes. Cruz’s finish was also typical, but for a different reason: he was, and is, outperforming his polls. Cruz’s pre-election polls were 39.0 ± 1.2%, and he ended up with 48% of the vote. In previous states, Cruz has overperformed by a median factor of 1.2. Either Cruz’s supporters are exceptionally committed, or he is the beneficiary of anti-Trump votes liberated from their previous first choices, or undecided voters break hard for him, or some combination of the three. In Wisconsin he may also have benefited from the fact that trailing candidates like Kasich often underperform their polls when it is time to vote.
Where is the national race now? The current 6-national-poll median (March 29-April 6) is Trump 39.5 ± 1.2%, Cruz 31.0 ± 2.1%, Kasich 19.0 ± 1.1%. If we were to apply a 1.2-fold bonus to Cruz’s numbers to allow for his overperformance, the corrected numbers are Trump 39.5%, Cruz 37.2% – extremely close. Either way, Cruz has risen quite a bit in the last month, and national opinion is now closely divided.
I have updated the polls-only snapshot of the remaining Republican primaries through June 7th, when voting ends. As I pointed out months ago in The New Republic and The American Prospect, Republican rules are complex and tilt the playing field toward the front-runner, even if he/she doesn’t get a majority of the popular vote. Therefore it is essential to emulate the state-by-state delegate rules with close attention to quantitative accuracy.
Even after getting the rules right, this is a challenging calculation for three reasons: (a) many states lack polls; (b) Cruz overperforms his polls; and (c) delegates may not follow the rules. Today I describe one way of dealing with all of these issues.
For those who just want the bottom line: Since my last update, a poll-based snapshot has moved – in Trump’s favor. If current polls accurately measure voter behavior, then Donald Trump would get a median of 1,356 delegates – almost 120 more than the 1,237 he needs for a first-ballot victory at the national convention in Cleveland. For this probability to drop to 50%, his national lead would have to drop by 8.0% – this is Trump’s Meta-Margin, a measure I have previously developed for general-election Presidential races. However, if Cruz’s overperformance continues, Trump’s lead would narrow considerably, to a count of 1,280 delegates and a Meta-Margin of 2.0%. After allowing for Cruz’s potential overperformance, the probability of a Trump majority is 70% – probable but uncertain. Under such closely divided conditions, the outcome won’t be known until the last primaries, on June 7th.
And now I will explain at length. [Read more →]