The reason the 1960 election didn’t work under the model was because it was a stolen election.
That may or may not be true. However any model, no matter how well constructed is only an approximation of what we believe reality will be. Other factors, such as chance, as well as the interaction of human factors such as emotion play a role.
As a Christian, I believe God has a plan as well, though I don’t presume to know or predict what it is.
1960 was going to be a close election, that allows many factors, to include human corruption and failings to have an outsized impact on the outcome.
This electoral environment, if you look at comparative enthusiasm from the turn out for each party, favors the Republican nominee.