I think the difference in opinion is caused by Taleb modelling the election as though all of the uncertainty is caused by the fact that people might change thei

I think the difference in opinion is caused by Taleb modelling the election as though all of the uncertainty is caused by the fact that people might change their minds, whereas Silver is also including the uncertainty from polling errors. Silver's predictions fluctuate a lot as time passes. Taleb is assuming that all of these fluctuations are caused by the electorate changing who they're going to vote for. Then he says "if you knew people's opinions were as volatile as this, you shouldn't have been so confident earlier!", or words to that effect. If lots of people will change their minds, then early polling won't be very informative about the final result. But the fluctuations in Silver's predictions are actually caused by his changing certainty about how accurate the polls are. Silver does take into account that people might change their minds, but this isn't the cause of most changes in his predictions. So people actually change their minds a lot less often than Taleb's model of Silver's model suggests. This is why Silver can make strong predictions early on.