The Primary Model is a political forecasting method used to assess the chances of competing presidential candidates, based on voting patterns from presidential primaries.
It was launched in 1996 and, used retroactively, has allegedly "picked the winner in all but two elections since 1912," Professor Helmut Norpoth, its developer, states, as quoted by the Washington Times.
In March, 2016, it gave Trump an 87% chance of beating Hillary Clinton and now, Norpoth says, "it gives Trump a 91% chance of winning in November."