They were pretty clear about the level of uncertainty leading up to the election. They said the data they were seeing and Donald Trump winning could both occur

They were pretty clear about the level of uncertainty leading up to the election. They said the data they were seeing and Donald Trump winning could both occur in a random universe slightly more than flipping a fair coin twice and both times getting tails (29%). Probability exists to quantify uncertainty, not to predict the future (though this can help). One thing is clear - we don't live in a random universe, and there are concrete biases present in the way we collect election data. FiveThirtyEight carefully avoids and accounts for many of these sources of uncertainty. For example, herding of polls at the end of an election and the unusually high percentage of undecided voters at the end of the election.