What should the number have been, then? The final results were essentially a tie with Trump winning the tie breaking coin toss. So 50/50 is right in hind sight. Te systemic error could just have been as easily in Clinton's favour as Trump's, so the number should have been smaller than 50% for Trump. Maybe not as small as 28%, but they weren't far off, IMO.

The model predicts a chance of winning, it doesn’t reflect the final vote percentages. In other words, a win is a win, regardless of whether it’s by a few votes or a landslide. That’s what the 80/20 represented. This is different than the polling averages. Though, electoral vote percentages are captured in 538’s model — they show a spread of possible win scenarios based on many numbers of runs of the model.

One could imagine such a non-linear model, but one wouldn't consider it well-behaved or even particularly useful for aiding one's understanding of reality.

The votes coming down to a dead heat doesn't mean that, the day before, they were equally likely to win. Suppose there were 100 possible futures. In 90 of them, Alice wins, by a little or a lot. In 8 of them, Bob barely wins, and in 2, Bob wins comfortably. Maybe this is determined by rigged dice or something, to make it strictly mechanical: there's 100 possibilities, and we know what they are and how they're distributed.

Just because you end up in the 9/100 future doesn't mean that the "real" probability was 50%. It's weak evidence that Bob's win scenarios mostly didn't involve blowouts.

It's like barely winning a sprint against Usain Bolt: maybe he had an injury midway through. Doesn't mean that he and I were equally likely to win.

The "score" was 1,405,280 to 1,382,536. That was the count in Wisconsin. Looks like a virtual tie to me.

That's the information we have, and it's real, so it's much more valid than any poll which poorly samples a few thousand people.

Maybe it was a fluke result. But that's unlikely because the other Midwestern states had similar results. But a fluke in which direction? You don't know, so it's even odds in both directions.