That's not their method at all. They're very insistent on the fact that voting shifts or errors between states are generally highly correlated. That's exactly

That's not their method at all. They're very insistent on the fact that voting shifts or errors between states are generally highly correlated. That's exactly why their probability forecasts tend to be more conservative than other forecasts. If you see a whole lot of possible paths for a candidate, and assume the errors are random, then that candidate will almost certainly win. If you know they might be correlated, then you know that a huge number of paths may shift at once.