The direction battleground states swing in the presidential election is likely to be heavily influenced by their level of educational attainment, a measure that's shaping up to be one of the top demographic fault lines in this campaign.
College-educated voters made up almost half the 2012 electorate nationally, but some states are more educated than others. They range from Massachusetts, where nearly 41.5 percent of those 25 years or older have a college degree, to West Virginia, where 19.6 percent do.
Some of the states viewed as key battlegrounds have relatively higher levels of schooling and could well prove to be out of Donald Trump's reach. Surveys have shown that Hillary Clinton's candidacy is favored by the more educated voters, while Trump is more popular among those who don't have college degrees.
John Della Volpe, director of polling at the Harvard University Institute of Politics, said the axiom of "demographics is destiny" that was often applied to the 2008 presidential campaign is also potentially playing out in this one.
"The factors important in determining the electoral destiny this time around are closely related to class and education," he said. "When looking at which states will break from their traditional patterns, understanding the percentage of voters who are college and non-college-educated whites is critical."
Colorado is a textbook example. The state ranks third in the nation for share of those 25 and older with a college degree. At 39.2 percent, it's well above the national average of 30.6 percent.
Clinton has held a consistent lead in the rapidly growing western state most of the summer and early fall, so much so that her campaign stopped advertising there in late July.
The Colorado race appears to have tightened in recent weeks, as it has nationally and in other key states. A CNN/ORC poll taken Sept. 20-25 showed Trump leading Clinton by 1 percentage point among likely voters in a four-way race that includes third party candidates.
Clinton's strong polling position in Virginia, where she hasn't advertised since early August, also correlates with educational attainment. That state ranks seventh nationally for share of those 25 and older with a college degree.
New Hampshire, which ranks ninth, has also been a relatively strong polling state for Clinton. But it's also a heavily white state packed with younger voters, both demographics groups where she has struggled to find support.
The two battlegrounds where Trump holds polling advantages, Iowa and Ohio, are tied at No. 36 in the college degree rankings. Both states voted for President Barack Obama in 2012, although Clinton has struggled to gain ground in them.
One other battleground state with a low proportion of college graduates is Nevada. Most of the recent polling there has shown Trump in the lead, although a Suffolk University poll of the state released on Friday showed Clinton leading by six percentage points when third-party candidates are included.
While there's no single demographic variable that can predict how a battleground state will vote in the presidential election, educational attainment and race are shaping up as two of the biggest differences in polling support for Trump and Clinton.
The most recent Bloomberg Politics national poll taken late last month showed Clinton winning the college-educated segment by 15 percentage points in a two-way race, 54 percent to 39 percent. Trump’s edge among those without a college education was 8 points, 50 percent to 42 percent.
Trump’s lead was almost 3-to-1 among white men with less than a college degree, 69 percent to 25 percent. Clinton’s advantage with white college-educated women was 55 percent to 37 percent.
That’s vastly different from what was recorded in the 2012 presidential election, when exit polling showed 47 percent of voters were college graduates. In that contest, Obama only narrowly beat Republican challenger Mitt Romney among college graduates, 50 percent to 48 percent.
"It seems quite likely Trump will do better among white, non-college grads than his predecessor, but the question is how much better," said Peter Brown, assistant director of the Quinnipiac University poll. "A state that has disproportionately more college graduates appears more likely to vote for Secretary Clinton than Mr. Trump."
A Quinnipiac University national poll released Sept. 26 found Clinton leading Trump among college educated voters, 49 percent to 36 percent. Trump led among those without college degrees, 49 percent to 39 percent.
The share of the college-educated vote received by the Republican nominee and the Democratic nominee also tended to be relatively close in the two most recent elections before 2012.
Obama in 2008 won among both those who did and did not graduate college by almost identical margins over Senator John McCain of Arizona (53 percent to 45 percent, and 53 percent to 46 percent).
President George W. Bush beat then-Senator John Kerry of Massachusetts in 2004 among those with no college degree, 53 percent to 47 percent. Among those with college degrees, the two men tied at 49 percent.
Della Volpe, the Harvard pollster, said his study of millennial voters has shown "educational attainment is a key predictor of attitudes about candidates" and views about the nation.
Young Americans without a college degree are far more likely to believe the American dream is dead, he said, compared to those with a degree or enrolled in college.
"There's no bigger predictor on whether a young voter believes in the American dream than whether or not they have a college degree," he said. "Variables such as race, gender and age are far less important than educational attainment."