With the Wisconsin State Capitol building dome behind him, President Barack Obama speaks at a campaign event, Nov. 5, 2012, in downtown Madison, Wis. (Carolyn Kaster/AP Photo)

Barack Obama has inched to a slim advantage in the closing days of the 2012 presidential race, breaking out of a long-running deadlock with Mitt Romney to a 50-47 percent contest in the final-weekend tracking poll by ABC News and The Washington Post.

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While still lacking a majority in vote preference, Obama has reached 51 percent job approval, matching his best this year; extended his advantage in better understanding Americans' economic problems; and moved to within a single point of Romney in trust to handle the economy, reversing a 9-point Romney lead on the central issue of the campaign.

See PDF with full results and charts here.

In another potentially important measure, regardless of their own preference, 55 percent of likely voters expect Obama to win re-election, down from its pre-debate peak in late September but a majority steadily since last March. A little over a year ago, by contrast, when economic discontent was at full boil, just 37 percent expected Obama to win.

The outcome is far from assured in a race that has been the closest on record, by some standards, since the start of pre-election polling in the mid-1930s. Turnout is critical, with Obama's slight edge relying on robust participation by Democrats and minorities and a competitive showing among independents. But there's some evidence for it: his supporters are more strongly enthusiastic than Romney's by an 8-point margin in this poll, produced for ABC by Langer Research Associates. That's numerically the widest enthusiasm gap since early September.

TREND - The race between the two has been locked for months, averaging a dead heat in fall polling by ABC and the Post. Romney took the momentum after the first debate and extended it as recently as a week and a half ago. He reached his apex Oct. 24, a numerical, 3-point edge in vote preferences overall, including a 19-point lead among independents.

But that advance stalled, with Obama pushing back in key groups and on the crux issues of managing the economy and economic empathy. By early last week - before Hurricane Sandy struck the East Coast - the gap among independents, potential swing voters in national elections, had shrunk to single digits, and Romney's gains on the key issues had halted.

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The trend in these closing days, in Obama's direction, has been slight but consistent. In a rolling four-day average, vote preferences since Thursday have gone from Romney +1, to a dead heat, then Obama +1, now Obama +3. Today's 50 percent for Obama matches his high among likely voters, last seen July 8. Romney's 47 percent is his lowest, numerically, since Oct. 13.

The 50-47 percent difference is not statistically significant at the customary confidence levels used in survey research. But it's likelier than not to reflect a slight Obama advantage, given this survey's models of who's most apt to vote.

This is in a race that's been heart-stoppingly close. The average difference between Obama and Romney in ABC/Post polling since September has been one-tenth of a percentage point, numerically the closest in comparable periods in pre-election polls since their start in 1936. And it's the first race since 1960 in which neither candidate has held majority support at some point, adjusting for third-party vote.

Romney's key shortfall on issues has been his difficultly closing the sale on the argument that he'd outperform Obama in handling the economy. They're at essentially a dead heat on this issue - Romney +1 - and Obama leads by 8 points on economic empathy, that is, better understanding Americans' economic problems. It's Obama's largest lead on empathy since mid-October, widening the past week and a half after squeezing to just +2.

THE CURVE - Regardless of the trends on issues specific to this election, Romney - and the Republican Party more broadly - are on the difficult side of an inexorable demographic curve, the shrinking dominance of white voters in national elections.

Romney leads among whites by 15 points, 56-41 percent - but they account for just 74 percent of likely voters, the same as in the 2008 exit poll and down from 90 percent in 1976. A quarter of likely voters are nonwhite, and they prefer Obama by a vast 76-20 percent, including by 96-3 percent among blacks and 61-31 percent among Hispanics. A similar equation led to Obama's election in 2008, when he lost whites by 12 points but won the presidency nonetheless. Turnout among racial groups thus is critical to this year's outcome.

Indeed, given the still-large size of the white voting population, the slightest improvement by Romney in this group - to 58 percent support among whites - would move him into a 1-point numerical edge, given the turnout proportions in this survey. Three candidates have done that well among whites since 1976, two of them incumbents - Ronald Reagan in 1984 and George W. Bush in 2004. The third was George H.W. Bush in 1988.

Romney's already at his required support level among many whites; specifically, white women who lack a college degree and white men regardless of their education. He leads in those groups by a combined 59-38 percent. It's among college-educated white women that he falls short; they now divide essentially evenly, 48-50 percent.

That difference carries across other measures. White women with college degrees approve of Obama's job performance by 52-47 percent; other whites disapprove by 59-40 percent. More-educated white women also are 12 points more apt than other whites to think that Obama better understands the economic problems of average Americans, and 11 points more apt to trust him over Romney to handle the economy.

These reflect gaps on social and economic issues in previous ABC/Post polls. College-educated white women are 14 points more likely than other whites to prefer Obama over Romney in trust to address "women's issues"; 16 points more likely to favor legal abortion (as does Obama, not Romney); and a slight 7 points more apt to see unfairness in the economic system as a bigger problem than over-regulation of businesses.

The difference among more-educated white women contributes to the gender gap overall: Obama +8 points among women, Romney +5 among men. For comparison, Obama finished +13 among women, +1 among men, in the 2008 exit poll. While the shares have shifted, the gap is nearly identical.

PERFECT STORM? - While the presidential debates clearly helped Romney, a lasting question of the election will be the effect, if any, of Obama's handling of the response to the damage wrought by Hurricane Sandy. The president has won broad approval for his work on the issue - 79 percent in ABC/Post tracking poll data, including a majority of Republicans.

Impact on vote preferences is less apparent. Fifty-one percent of likely voters call the storm a factor in their vote; about half as many, 23 percent, call it a major factor. By and large, though, people who call the storm a factor are those who fit the profile of Obama supporters in the first place.

Additionally, while Obama holds a 10-point advantage in trust to handle an unexpected major crisis, that's no different after the storm than before it.

That said, the disaster could have worked in subtle ways, for example raising the salience of the handle-a-crisis attribute. Among other results, Obama's image as a "stronger leader" than Romney rebounded in the past week, compared with their July levels. And Obama's core support has rallied; the number of likely voters who "strongly" approve of his job performance overall reached 35 percent in this survey, his highest since September 2009.

ENTHUSIASM - As Obama's strong approval has advanced, so has enthusiasm among his supporters - 69 percent say they're "very" enthusiastic about their choice, steady the last three days, up a slight 5 points from last week and on par with his strength of support in 2008.

Romney trails on this measure with 61 percent strong support, essentially unchanged since mid-October. Nonetheless that's far ahead of John McCain's strong support in 2008, and John Kerry's in 2004.

Romney's deficit in strong support is base-related, recalling the challenges he had winning support among some core Republican groups in the GOP primaries. Today, among Republicans who support Romney, 69 percent are strongly enthusiastic about him. Among Democrats who back Obama, strong support rises to 76 percent. Similarly, Obama's strong support among liberals is 7 points higher than Romney's among conservatives.

AND TURNOUT - The question is whether disproportionate enthusiasm produces disproportionate turnout. The campaigns have been hitting it hard; nationally 44 percent of likely voters say they've been contacted by one or both of the campaigns, and that soars to 69 percent in the eight states designated by the ABC News Political Unit as battlegrounds.

Romney's been keeping pace with Obama in voter contact overall, an improvement compared with McCain in 2008. In the battleground states, in particular, 48 percent of likely voters say they've been contacted by Obama's campaign - 51 percent by Romney's.

Turnout's not an issue for a sizable group: Using just the most recent (Sunday night) results, 31 percent of likely voters say they've already voted; more said they still intended to vote early. Looking at the past four nights among those who've voted early or planned to, preferences are identical, 50-47 percent, to those of Election-Day voters. That's far closer than Obama's 18-point advantage among early voters in ABC/Post polls in 2008. Then again, it's a far closer election.

CLOSURE - Whoever does win will take the reins of a sharply divided nation. Ninety-five percent of Republicans in this poll back Romney and 91 percent of Democrats favor Obama; independents divide closely 48-46 percent, Romney-Obama. Obama wins 85 percent of liberals and 57 percent of moderates; Romney, 80 percent of conservatives.

Those divisions are reflected, as well, in expectations of who'll win. Ninety-one percent of Obama supporters expect the president to win re-election; among Romney supporters, fewer, but still 71 percent, expect their candidate to prevail. That means that whatever the outcome Tuesday, many in this country will have not only their preferences but their expectations dashed - for whomever will govern, not an easy place to start.

METHODOLOGY - This ABC News/Washington Post poll was conducted by telephone Nov. 1-4, 2012, among a random national sample of 2,345 likely voters, including landline and cell-phone-only respondents. Results have a margin of sampling error of 2.5 points, including design effect. (Question 21 was asked Nov. 2-Nov. 4 among 1,769 likely voters; those results also have a 2.5-point error margin.) The survey was produced for ABC News by Langer Research Associates of New York, N.Y., with sampling, data collection and tabulation by Abt-SRBI of New York, N.Y.

Partisan divisions, Democrats-Republicans-independents, are 35-29-32 percent among likely voters; they were 39-32-29 percent in the 2008 exit poll. The ABC News Political Unit defines the "battleground" states as Colorado, Florida, Iowa, Nevada, New Hampshire, Ohio, Virginia and Wisconsin.