[cgbg]

Pollsters must make assumptions about turnout.

If their assumptions are wrong their polls will be wrong.

Easy peasy!

They polled D+8 to D+10, actual was D+4.

[fhayek]

So, if the pollsters had used D+4, they would have been very close. Listen, 2008 it was D+7. 2012 it was D+6. These were outliers, fueled by an African American nominee (who would naturally create AA turnout). Anyone who thought that Hillary would generate that wasn't paying attention. She wasn't black, she wasn't charismatic, and she had royally pissed-off a huge portion of her left wing base by her treatment of Bernie Sanders. We all recognized that around these parts. Odd that the professionals couldn't see it.