The 6 Most Important Numbers to Watch Tuesday Night

The minority vote, the blue wall, and the mandate: the key figures that will determine the outcome of the presidential race

After a campaign of unprecedented expense and duration, the third presidential contest in the past four to divide America almost exactly in half is now almost in the hands of the voters. With polls showing President Obama holding a small lead over Mitt Romney in key battleground states, but locked in a virtual dead-heat nationally, here's a look at the factors that could decide who gets the 270 Electoral College votes needed to win the race for the White House on Nov. 6.

1. What is the minority share of the vote?

Key number: 26% or more

Obama is likely to win about twice as large a proportion of the non-white as the white vote. How many whites and non-whites vote is therefore the single most important question in the election, both nationally and in the key swing states.

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Since 1992 the non-white share of the vote has grown steadily at about three percentage points with every election, from 12 percent when Bill Clinton was first elected, to 26 percent for Barack Obama's election in 2008. If the trend has continued this year, it will make Obama's path to reelection much easier. But if minority turnout lags, or turnout among older conservative whites soars -- as it did in the 2010 mid-term election--it will make the math much more favorable for Romney. Youth turnout is critical here too, because about 40 percent of the Millennial Generation are non-white, compared to only about half that among seniors.

Obama's team projects a 27 percent or 28 percent minority share of the vote; Romney's advisers expect it to remain stagnant at 26 percent, or perhaps even decline. Such small shifts could have huge implications for battleground states with rapidly growing minority populations, including Nevada, Colorado, Virginia, Florida and maybe North Carolina. The challenge for Romney is that even though surveys show enthusiasm about voting lagging among Hispanics (who are the fastest-growing minority group), Census Bureau data show that minorities now comprise 29 percent of all those eligible to vote. So, even if the percentage of eligible minority voters who turn out to vote is lower than in 2008, their share of the total electorate could still increase.

2. Can Obama hit the 80/40 mark?

Key numbers: 80 percent of 26 percent + 40 percent of 74 percent

Obama's formula for success can be succinctly expressed. If minorities constitute at least 26 percent of the vote (as they did last time), and he wins at least 80 percent of their cumulative votes (as he did last time), he can win a national majority with support from only about 40 percent of whites. But there's no guarantee he can reach even that modest number. Obama last time won 43 percent of whites, but Democrats captured only 37 percent of them in the 2010 Congressional elections, according to exit polls at the time. Obama had 39 percent among whites in two polls released on November 4. That would probably lift him just over the 40 percent marker when undecideds are allocated -- but with achingly little margin for error.

Other factors could give Obama more breathing room. The share of whites he needs would decline to just above 38 percent if minorities rise to 27 percent of the vote and he wins 82 percent of them, both of which seem possible. All of this means that Romney could run as well among white voters as any Republican challenger ever -- and still lose. Whatever happens, the election is likely to send Republicans an irrefutable message about the long-term demographic implausibility of building their coalition almost entirely from white voters in a country that is now nearly 40 percent non-white.

3. Can Obama hold his gains among working-class whites in the Rustbelt?

Key number: 10 percentage points

As I've written on Quartz before, the central paradox in this election is that while Obama is facing a potentially historic repudiation among working-class white voters overall, those same voters in a few Midwestern states could be the ones who get him re-elected.

Nationally, the November 4 Pew Research poll, like many others, showed Obama winning just 33 percent of white men without a college education and only 38 percent of non-college white women, the so-called "waitress moms". That would be the weakest performance for any Democratic nominee among those voters since Walter Mondale was buried in the Ronald Reagan landslide of 1984. Yet in the key Midwestern battlegrounds of Iowa, Wisconsin, and Ohio, Obama is running about 10 percentage points better among the blue-collar white men and as much as 18 percentage points better among the waitress moms. (The same pattern is present, to a lesser extent, in Michigan, which Romney had hoped to bring into play.)

The reasons for that difference are several -- the Midwest's relatively stronger economic recovery, the popularity of Obama's bailout of the car industry, and the cultural resonance in the region of Obama's attacks on Romney as a plant-closing corporate raider. But the effect is singular: so long as the president can hold his blue-collar Rustbelt advances, he remains the favorite to reach 270 Electoral College votes.

4. Can Romney breach the "blue wall"?

Key numbers: 18 and 242

If Obama wins Ohio, the only realistic way for Romney to win is to crack what I've called the "blue wall" -- the 18 states that have voted Democratic in each of the past five presidential elections. Here's why: the blue-wall states, which include the 11 states from Maryland to Maine (except New Hampshire); the three West Coast states plus Hawaii; and Michigan, Minnesota, Illinois and Wisconsin in the Upper Midwest, offer a combined 242 Electoral College votes (including the District of Columbia). If Obama holds that 242, adds the five votes from New Mexico (that both sides assume he will), the six from Nevada (which appear increasingly solid in his corner) and Ohio's 18, that gives him 271, regardless of what happens in any other swing state.

That explains why Romney is not only fiercely contesting Wisconsin (which has supported Democrats in every election since Reagan's win there in 1984), but is also making a late play for Pennsylvania (which hasn't voted Republican since 1988) and Minnesota (which hasn't backed the Republicans since 1972). If Obama wins Ohio, and barring a huge surprise in Nevada, Romney can't win without snatching one of those three states.

5. Can Romney retake the Sunbelt?

Key numbers: 5 and 72

Obama's big geographic breakthrough in 2008 was rooted in changing demographics. He captured a succession of diverse, growing Sunbelt states -- including Virginia, North Carolina, Florida, Colorado, and Nevada -- that had voted Democratic only rarely over the previous 40 years. He did this mostly because those five states' electorates, with 72 Electoral College votes between them, have been reshaped by two titanic social forces that Obama himself embodies: rising education levels and increasing diversity.

But now polls show Obama facing a more precarious situation in all of those states (except Nevada) than in the central Rustbelt battlegrounds of Ohio and Wisconsin. It's mainly because, compared to the Rustbelt, Obama faces much weaker numbers among working-class whites in these Sunbelt states--where his attack on Mitt Romney's days as a corporate raider and harbinger of industrial decline doesn't detonate as powerfully.

Obama's disadvantage among working-class voters in these states is big. Recent polls in North Carolina, Colorado, Florida and Virginia each put Obama below 30 percent among non-college white men. To overcome these deficits he needs a big turnout from both minorities and suburban, college-educated whites, especially women, who he's courting on social, more than economic, issues. As Democrats face a systemic decline among working-class whites (at least beyond those few Midwestern states), that upstairs-downstairs coalition of white-collar whites and minorities represents the party's future. But in this election several of the Sunbelt states that most embody that "coalition of the ascendant" could snap back to their Republican leanings from the 1970s to 2004.

The problem for Romney, however, is that winning all of these Sunbelt battlegrounds (apart from Nevada) is a necessary but not sufficient condition for winning the election overall.

6. Can anyone win a mandate to govern?

Key number: 3 percent

From any angle, the narrowness of the divide evident in this election is extraordinary. Today it appears entirely possible that either Obama or Romney will win the popular vote by less than three percentage points. If the race is indeed that close, it would mark the third time in the past four presidential elections that a winner was decided by that amount or less.

That hasn't happened since the five elections during the Gilded Age from 1876-1892, another period defined by epic economic and demographic change -- and by a political system that proved incapable of responding to it. In 2004, George W. Bush won reelection by just 2.4 percentage points: the smallest margin of victory, as a share of the popular vote, ever for a re-elected president. Even if Obama wins the popular vote, his margin might be even smaller than that. There's also the more distant possibility that he could become the first incumbent ever to lose the popular vote while winning the Electoral College.

Either way, the overriding message of the election is likely to be that while the two parties are more than ever poles apart, the country itself remains closely divided. That means that after the votes are counted, the common challenge for whoever wins will be to build a working majority for change -- no easy feat in a nation that remains bitterly, and durably, fractured along lines of gender, education, ideology, region and race.