"We don't have a Trump variable in the model."
source: http://money.cnn.com/2016/05/26/news/economy/hillary-clinton-beat-donald-trump-moodys/index.html
It is variable as part of an algorithm. For example, in their model, they don't have a if (candidate==trump) {}.
What they mean, implicitly, is that Trump is such an odd and extravagant candidate that it is complicated to include that in their calculation and to predict what the outcome is going to be, since their algorithm only calculates the odds according to the political party of the candidate.
