Why were the election polls so off?

How evenly divided is the nation? Out of 120 million votes cast this election, the candidates each got a little less than 60 million in the popular vote, with Hillary Clinton ahead by about 200,000. 

CBS News’ Anthony Mason showed us how Donald Trump scored his upset

The Donald Trump victory was built on several key pillars. Trump won men 53-41, but lost women by a similar margin.

His greatest strength came from whites without a college degree. He had nearly a 40-point edge among those voters.

When we asked voters the most important quality they were looking for? Number one was a candidate who can bring about change. Donald Trump won 83 percent of these voters. 

After the release of the “Access Hollywood” tape, some Republican leaders un-endorsed Trump.  And it looked like there could be significant defections from the Republican ranks. It didn’t happen. He won 81 percent of conservatives and white evangelicals. Nine out of 10 Republicans voted for Trump.

At the same time, Clinton under performed with three key groups in the Democratic coalition. 

She won 55 percent of young voters, but President Obama took 60 percent four years ago. She won 88 percent of the African American vote, Mr. Obama had 93 percent in 2012. Even with the Hispanic vote, where early voting suggested new strength for Clinton, she polled only 65 percent. Mr. Obama polled 6 points higher.

In the end, Republicans came home. Democrats it seemed stayed home. 

Finally, 13 percent of voters made up their minds in the last week, and they broke strongly for Trump in key battleground states.

He won a majority of late deciders in Pennsylvania, Wisconsin, Michigan and Florida. The biggest margin in Wisconsin 58-31 percent. And that’s why Donald Trump had surprising strength in those states. 

So how did the polls lead us astray? Including our CBS News poll--which is considered to be one of the best in the industry?

 Anthony Salvanto, our director of elections -- in other words, our polling expert, has an answer. 

First of all, the polls got the popular vote nearly right -- but missed badly on how the individual states would go in the electoral vote. Salvanto says Democrats said they would go to vote in polls, but didn’t actually turn out on Election Day,