This is, from my recollection, an incorrect assessment of Silver’s methodology. He runs (continuous?) Monte Carlo simulations over his inputs, and when he says

This is, from my recollection, an incorrect assessment of Silver’s methodology. He runs (continuous?) Monte Carlo simulations over his inputs, and when he says that there's an 80-20 chance in favour of candidate O, he's saying that 80% of the simulations resulted in a win for candidate O, not candidate R.