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Predicting elections is a game of numbers; the unemployment rate, economic growth, a president's approval ratings. And each campaign must also run the numbers on the voters themselves. That is, what types of people - white males, the young, Latinos - can be persuaded to come to the polls in November?
Here's NPR's Mara Liasson with a report on that set of numbers and on how the changing profile of the electorate could affect the outcome of this year's race.
MARA LIASSON, BYLINE: There are two big factors that will determine the outcome of the presidential election: the economy and demographics. The economy is weak and doesn't look likely to improve by much. The makeup of the electorate, on the other hand, is highly dynamic and it's continuing a trend underway for years - a rapid rise in the number of people who are not Anglos, in the population and at the polls.
ALAN ABRAMOWITZ: That percentage actually doubled just between 1992 and 2008.
LIASSON: Alan Abramowitz is a political scientist at Emory University.
ABRAMOWITZ: It went from 13 percent of voters to 26 percent of voters. And without that trend it's very unlikely that Barack Obama would have won the 2008 election.
LIASSON: And Mr. Obama needs that trend to continue and possibly even accelerate in order to win a second term. That's because the president's share of the white vote is dropping.
Four years ago, he got 43 percent of the white vote. Now polls show him with only about 38. His gender gap advantage with white women has shrunk. And among whites without a college degree, he only gets about one-third. To offset that, he not only has to win the minority vote, Abramowitz says, he also has to make sure non-white voters make up a bigger share of the overall electorate.
ABRAMOWITZ: In 2008, according to the national exit poll, non-whites made up about 26 percent of the voters. And if they can get that up to, say, 28 percent, then Obama could probably come close to winning, maybe even win the popular vote while losing the white vote by 20 points. I'd say it's doable, but I don't think it's, you know, going to happen by itself.
LIASSON: In this election, mobilization matters more than persuasion because there are so few undecided voters; probably less than 10 percent. So both sides are focusing more on turning out their base.
It's why the president has been targeting Hispanic voters with ads like this one, featuring talk show host Cristina Saralayhee, known as the Latina Oprah.
(SOUNDBITE OF A POLITICAL AD)
CRISTINA SARALAYHEE: (Spanish language spoken)
LIASSON: The more non-white voters the Obama campaign can turn out, the more white voters he can afford to lose. And in key battleground states the reverse is true for Romney, says Matt Barretto with the polling firm Latino Decisions.
MATT BARETTO: So if you take a Nevada, Latinos could be anywhere as high as 15 percent of the electorate on Election Day. Or they could be as low as eight percent. And that is a real challenge for the president, that he wants those Latino numbers to be as high as possible, because he's winning the vote right now, two-to-one, three-to-one. And Romney needs to chip away at that, and that's the challenge for Republicans.
LIASSON: As Romney famously told a crowd of donors this spring, the president's big lead with Hispanics, quote, "spells doom for us." In the longer term, he may be right, but this year he's betting he can beat the trend by boosting the white vote in key states.
ABRAMOWITZ: I think the main focus of the Romney campaign has been, and will probably continue to be, on trying to energize and turn out the conservative white base of the Republican Party and hope that they can generate a high enough margin there, to overcome Obama's advantage among non-whites and white liberals.
LIASSON: Romney has the easier turnout task. Whites historically turn out to vote in higher numbers than minorities. They're expected to be more than 70 percent of the November electorate even though they're only 63 percent of the population. And Romney has a powerful force working in his favor this year: the underlying fundamentals of a bad economy.
JOHN MORGAN: The analogue that most people will look at is 1980, where you had an incumbent president who was very much suffering from a weak economy.
LIASSON: John Morgan is a Republican demographer.
MORGAN: People had made up their minds in the springtime that they were not only willing to look at somebody other than President Carter, that they were in fact going to vote against him. And so, you could have a situation here with President Obama, where the damage is done on the economy, and those voters that have moved away from him have moved away.
LIASSON: And that's what Republicans are banking on, that the fundamentals of the bad economy keep the president stuck where he is today; at under 50 percent approval and less than half of the vote.
Of course, no one is suggesting that Mr. Obama is as bad off as Jimmy Carter was - with a hostage crisis, stagflation and approval ratings in the'30s - or that Mitt Romney can repeat Ronald Reagan's performance as a candidate, but Republicans are looking to continued bad economic numbers to finally tip this dead heat election in Romney's direction.
Mara Liasson, NPR News, Washington.