Clinton’s success is built on holding together those blocs of voters. She does not, for example, enjoy the same support among African-Americans as Obama, the first black U.S. president. Diminished support among blacks, coupled with a large drop in black turnout, would hurt the Democrat.
If black Democratic turnout drops by 15 points nationally, for example, Clinton’s odds of winning drop to about 72 percent, by a projected margin of just 32 Electoral College votes. A drop of 20 points would reduce the odds of a Clinton victory to little more than a coin toss, according to the project.
Now if you're a Hillary supporter, you might not think much of a drop in her probability of winning from 95 percent to 90 percent. You might even laugh at people like me for finding any encouragement from it.
But here's the real reason Hillary should be worried: Over the past week, just about every trend has been in Trump's direction, and because we're so close to the day of actual voting it's very difficult to get a sense from the polling averages what the mood of the electorate will be on Tuesday.
Remember, tracking polls measure the rolling average of several days to try to tell you what's happening in the minds of voters. That's a useful moderating feature in the sense that it doesn't give you an exaggerated picture because of one day that might be an outlier. But where a tracking poll might fail to give you the complete picture is in a situation where things really are changing quickly and dramatically.