[dllthomas]

You're misreading or confused or something. The 538 piece points to a ~10% swing away from the (in the case of black voters) 82% that favored Hillary. This is very different from a swing all the way to a 10% preference for Trump. A bigger turnout by (these) minority voters, assuming they cast votes even vaguely in line with this polling, is more votes in Biden's column than Trump's. That's bad news for Trump.

[dsaavy]

I think you're misreading my statement, it's a 10% swing in the direction of Trump, not a 10% overall preference for Trump. From 82% favoring Hillary to 71% favoring Biden for black voters. That's a 10% change towards Trump's direction. If 16 million black voters participated in 2016 then that's around 13.1 million votes for Hillary and 2.9 million for Trump. If polling is correct this year and we see around similar turnout (not even an increase), then it'll be around 11.3 million votes for Biden and 4.7 million for Trump. So a 1.8 million vote swing in the black vote.

That's just a really rough calculation and doesn't account for the Hispanic vote either in that article.

[dsaavy]

Apologies, my above explanation is actually wrong. The article is actually referencing the margin of the candidate. So it was a 82 point margin between Clinton and Trump in 2016, which is still difficult to interpret because it doesn't mention if this includes 3rd party votes. But assuming 98% of voters voted Clinton or Trump, this would mean that 90% of black votes went to Clinton and 8% went to Trump in 2016.

This would then mean that if 98% vote Trump or Biden in 2020, we'll see something like 84% of the black vote for Biden and 13% of the black vote for Trump. A 5% overall change using 2016 voter participation numbers is still somewhere around 700,000 vote change in the black vote, which is certainly not insignificant. Adding in the change in the Hispanic vote (a margin change from 37 points in 2016 to 23 this year), this could certainly change swing state outcomes.

[dllthomas]

But unless I'm misunderstanding something, the change in approval is already factored into the current predictions. If there is a greater than expected turnout by a group of people voting - in aggregate - more for Biden than for Trump, then that favors Biden relative to the current predictions. So that's not going to be a reason for a surprise in the other direction.

There are plenty of reasons our predictions might not match reality, but they're not going to be wrong in that direction for that reason.