WASHINGTON -- As the presidential campaign enters its final weekend, the polling snapshot remains essentially unchanged. President Barack Obama and Republican presidential nominee Mitt Romney remain essentially deadlocked in most national surveys, but polls in battleground states continue to show Obama with just enough of an edge in states whose electoral votes would add up to more than the 270 needed to win.

With just four days remaining until the vote is counted, poll watchers should be on alert for any developing trends that might signal a late shift in voter preferences. As of this writing, there are a few hints, but none that rise to the level of statistical significance.

The margin separating Obama and Romney in the national polls clearly narrowed following the first presidential debate on Oct. 3. Since the middle of October, however, the HuffPost Pollster poll tracking model, based on all available public polls, has shown a roughly even race for the national popular vote.

Over the past week, the national estimate has tipped to Romney by about a half a percentage point, randomly varying up or down within a range of roughly +/- 0.3 points with each successive update of the model. As of this writing, however, Romney's edge is at the low end of that range. The larger point: the current razor-thin margin is just one-tenth of 1 percentage point different, as of this writing, from what the model estimated on Oct. 16, the day of the second debate.

For the moment, at least, nearly all of the recent national poll releases are showing either a tie or a slight Obama edge. Only two polls -- the Rasmussen automated tracking poll and the last update of the Gallup Daily tracking released before Hurricane Sandy made landfall -- give the edge to Romney. Of course, given the close nature of the race and the margins of sampling error associated with each poll, none of the individual surveys can identify the true leader in the national popular vote with statistical confidence.

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The national popular vote estimate produced by the Pollster tracking model takes pollster "house effects" into account, which means it works to bring the results of individual pollsters into line with industry averages. Thus the presence or absence of polls that consistently lean to Romney (such as the Gallup Daily and Rasmussen tracking) or to Obama (such as the Zogby Internet poll) will not alter the daily estimates, as they might with a simpler average.

We have also entered more than two dozen new polls into the Pollster database over the last 24 hours, most from the key battleground states, but the estimates of the polling snapshot distilled from these surveys looks about the same as it has for the past three weeks. Obama continues to maintain leads of 2 to 4 percentage points in four states -- Ohio, Iowa, Nevada and Wisconsin -- that when combined with other states where he leads by larger margins, add up to 277 electoral votes, just over the 270 needed to win.

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Four more states representing a total of 55 electoral votes -- Colorado, New Hampshire, Virginia and Florida -- currently show margins of less than 2 percentage points separating the candidates, with all but Florida currently tipping slightly in Obama's favor. To win the election, Romney would need to sweep all four of these states plus either Ohio or both Nevada and Iowa.

Over the past two weeks, the model's estimates have remained reasonably stable, with Obama doing slightly better in most states, as of this writing, compared to what our estimates were showing on Oct. 16 -- but with Romney having gained slightly in two of the most important states, Iowa and Ohio.

Obama's Iowa and Ohio margins remain relatively small, though given the high volume of polls in the past few weeks, the model reports very high statistical confidence that Obama would lead if polls are accurate and all votes were cast today. That statistical confidence does not allow, however, for the possibility that polls might be collectively wrong by enough to reverse these margins, which past history says is a small but real possibility.

The coming weekend will feature the final releases from a long list of prominent pollsters, which will give us our last indication of late trends, should any appear. For the moment, however, the polling snapshot remains mostly the same.

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  • Situation Room

    May 1, 2011: President Barack Obama and Vice President Joe Biden, along with members of the national security team, receive an update on the mission against Osama bin Laden in the Situation Room of the White House, May 1, 2011. Seated, from left, are: Brigadier General Marshall B. "Brad" Webb, Assistant Commanding General, Joint Special Operations Command; Deputy National Security Advisor Denis McDonough; Secretary of State Hillary Rodham Clinton; and Secretary of Defense Robert Gates. Standing, from left, are: Admiral Mike Mullen, Chairman of the Joint Chiefs of Staff; National Security Advisor Tom Donilon; Chief of Staff Bill Daley; Tony Blinken, National Security Advisor to the Vice President; Audrey Tomason Director for Counterterrorism; John Brennan, Assistant to the President for Homeland Security and Counterterrorism; and Director of National Intelligence James Clapper. Please note: a classified document seen in this photograph has been obscured. (Official White House Photo by Pete Souza)

  • Head Pat

    May 8, 2009: President Barack Obama bends over so the son of a White House staff member can pat his head during a family visit to the Oval Office May 8, 2009. The youngster wanted to see if the President's haircut felt like his own. (Official White House Photo by Pete Souza)

  • Fist-Bump

    Dec. 3, 2009: President Barack Obama fist-bumps custodian Lawrence Lipscomb in the Eisenhower Executive Office Building following the opening session of the White House Forum on Jobs and Economic Growth, Dec. 3, 2009. (Official White House Photo by Pete Souza)

  • Mohawk Baby

    July 4, 2012: President Barack Obama holds a baby while greeting guests during an Independence Day celebration on the South Lawn of the White House, July 4, 2012. (Official White House Photo by Pete Souza)

  • The President

    July 26, 2012: President Barack Obama holds a Cabinet meeting in the Cabinet Room of the White House, July 26, 2012. (Official White House Photo by Pete Souza)

  • Oval Office Chase

    July 9, 2012: President Barack Obama runs around his desk in the Oval Office with Sarah Froman, daughter of Nancy Goodman and Mike Froman, Deputy National Security Advisor for International Economics, July 9, 2012. (Official White House Photo by Pete Souza)

  • First Couple

    June 13, 2012: President Barack Obama and First Lady Michelle Obama wave goodbye to President Shimon Peres of Israel on the North Portico of the White House following the Presidential Medal of Freedom ceremony and dinner in his honor, June 13, 2012. (Official White House Photo by Pete Souza)

  • Holocaust Museum

    April 23, 2012: President Barack Obama tours the United States Holocaust Memorial Museum in Washington, D.C., with Elie Wiesel, Nobel Peace Prize laureate and Holocaust survivor, and Sara Bloomfield, museum director, April 23, 2012. (Official White House Photo by Pete Souza)

  • Golden Girl

    June 11, 2012: President Barack Obama talks with Betty White in the Oval Office, June 11, 2012. (Official White House Photo by Pete Souza)

  • Venus In Transit

    April 24, 2012: President Barack Obama stops to view the moon and Venus before boarding Marine One in Boulder, Colo., April 24, 2012. (Official White House Photo by Pete Souza)

  • 'Sweet Home Chicago'

    Feb. 21, 2012: President Obama joins in singing "Sweet Home Chicago" during the "In Performance at the White House: Red, White and Blues" concert in the East Room of the White House, Feb. 21, 2012. Participants include, from left: Troy "Trombone Shorty" Andrews, Jeff Beck, Derek Trucks, B.B. King, and Gary Clark, Jr. (Official White House Photo by Pete Souza)

  • The Redeemer

    March 20, 2011: "The Obama family was scheduled to tour the Christ the Redeemer statue in Rio before dinner one night. But when heavy fog rolled in, they canceled the visit. After dinner, the fog had dissipated somewhat so they decided to make the drive up the mountain. It was quite clear when they arrived and then the fog started to roll back in. I managed to capture this silhouette as they viewed the statute one last time just before departure." (Official White House Photo by Pete Souza)

  • Water Fight

    June 11, 2011: "The top photograph shows the President having a water gun fight with his daughter Sasha on her birthday weekend at Camp David. Unbeknownst to me, David Lienemann captured a similar photo of the Vice President on the very same day." (Official White House Photos by Pete Souza and David Lienemann)

  • Christmas Card

    Dec. 11, 2011: President Barack Obama, First Lady Michelle Obama, and their daughters, Malia, left, and Sasha, right, sit for a family portrait in the Oval Office, Dec. 11, 2011. (Official White House Photo by Pete Souza)

  • MLK Memorial

    Oct. 14, 2011: President Barack Obama tours the Martin Luther King, Jr. National Memorial in Washington, D.C., Oct. 14, 2011. (Official White House Photo by Pete Souza)

  • Balloon Man

    Oct. 11, 2011: "This photograph by Chuck Kennedy has to catch your eye. It shows Guinness Book of World Records holder John Cassidy performing a balloon act for First Lady Michelle Obama in the Diplomatic Reception Room following a Let's Move event." (Official White House Photo by Chuck Kennedy)

  • Mandela

    June 21, 2011: First Lady Michelle Obama meets with former President Nelson Mandela of South Africa at Mandela's home in Houghton, South Africa, June 21, 2011. (Official White House Photo by Samantha Appleton)

  • Joplin, Mo.

    May 29, 2011: President Barack Obama greets Hugh Hills, 85, in front of his home in Joplin, Mo., May 29, 2011. Hills hid in a closet during the tornado, which destroyed the second floor and half the first floor of his house. (Official White House Photo by Pete Souza)

  • Daycare

    June 9, 2011: President Barack Obama greets children at a day care facility adjacent to daughter Sasha's school in Bethesda, Md., following her 4th grade closing ceremony, June 9, 2011. (Official White House Photo by Pete Souza)

  • Tucson Shooting

    Jan. 10, 2011: President Barack Obama and First Lady Michelle Obama walk towards the White House after observing a moment of silence for the victims of the Arizona shooting, on the South Lawn, Jan. 10, 2011. White House staff joined the President and First Lady for the moment of silence.(Official White House Photo by Chuck Kennedy)

  • What's Up?

    March 7, 2011: President Barack Obama, Prime Minister Julia Gillard of Australia, and members of the Australian and American delegations look up at the presidential seal in the Oval Office ceiling following their bilateral meeting, March 7, 2011. (Official White House Photo by Pete Souza)

  • Inclement Weather

    May 31, 2010: "The skies opened up on Memorial Day outside of Chicago. When the lightning began, the Secret Service told the President that it was too dangerous to proceed. He took the stage by himself and informed the audience that his speech was canceled and that for everyone's safety, they should return to their busses. Later, he boarded a few of the busses to thank them for attending and apologized for not being able to speak." (Official White House Photo by Pete Souza)

  • Power Walk

    July 20, 2010: President Barack Obama and British Prime Minister David Cameron walk across the South Lawn of the White House, July 20, 2010. (Official White House Photo by Pete Souza)

  • Oil Spill

    May 28, 2010: President Barack Obama and Lafourche Parish President Charlotte Randolf, left, inspect a tar ball as they look at the effect the BP oil spill is having on Fourchon Beach in Port Fourchon, La., May 28, 2010. (Official White House Photo by Chuck Kennedy)

  • Finally

    March 21, 2010: President Barack Obama, Vice President Joe Biden, and senior staff, react in the Roosevelt Room of the White House, as the House passes the health care reform bill, March 21, 2010. (Official White House Photo by Pete Souza)

  • First Pitch

    March 31, 2010: President Barack Obama practices his pitching form with personal aide Reggie Love and Jake Levine in the Rose Garden of the White House, March 31, 2010. The President threw out the ceremonial first pitch on opening day of the baseball season prior to the game between the Washington Nationals and the Philadelphia Phillies.

  • 3D

    Feb. 1, 2009: "During a Super Bowl watching party in the White House theatre, the President and First Lady join their guests in watching one of the TV commercials in 3D." (Official White House photo by Pete Souza)

  • Bo

    March 15, 2009: "The Obama family was introduced to a prospective family dog at a secret greet on a Sunday. After spending about an hour with him, the family decided he was the one. Here, the dog ran alongside the President in an East Wing hallway. The dog returned to his trainer while the Obama's embarked on their first international trip. I had to keep these photos secret until a few weeks later, when the dog was brought 'home' to the White House and introduced to the world as Bo." (Official White House photo by Pete Souza)

  • Moment Of Reflection

    Jan. 20, 2009: "President-elect Barack Obama was about to walk out to take the oath of office. Backstage at the U.S. Capitol, he took one last look at his appearance in the mirror." (Official White House photo by Pete Souza)

  • Snowball Fight

    Dec. 19, 2009: "Snowball in hand, the President chases Chief of Staff Rahm Emanuel on the White House colonnade. To escape, Rahm ran through the Rose Garden, which unfortunately for him, was knee-deep in snow." (Official White House photo by Pete Souza)

  • Nobel

    Dec. 10, 2009: President Barack Obama looks at the Nobel Peace Prize medal for the first time at the Norwegian Nobel Institute in Oslo, Norway, Dec. 10, 2009. (Official White House Photo by Pete Souza)

  • Presidential Trio

    Jan. 16, 2010: "President Obama had called on the two former Presidents to help with the situation in Haiti. During their public remarks in the Rose Garden, President Clinton had said about President Bush, 'I've already figured out how I can get him to do some things that he didn't sign on for.' Later, back in the Oval, President Bush is jokingly asking President Clinton what were those things he had in mind." (Official White House photo by Pete Souza)

  • Wounded Warriors

    Oct. 8, 2009: President Barack Obama watches as members of the National Naval Medical Center's Marine Wounded Warrior basketball team play on the White House basketball court, Oct. 8, 2009. (Official White House Photo by Pete Souza)

  • Shoot The J

    Oct. 8, 2009: President Barack Obama takes a shot during a game with Cabinet secretaries and members of Congress on the White House basketball court, Oct. 8, 2009. (Official White House Photo by Pete Souza)

  • Grand Canyon

    Aug. 16, 2009: President Barack Obama looks at the Grand Canyon in Arizona on Aug. 16, 2009. (Official White House photo by Pete Souza)

  • Ted Kennedy

    April 21, 2009: President Barack Obama and Sen. Ted Kennedy walk down the South Lawn sidewalk at the White House April 21, 2009. (Official White House Photo by Pete Souza)

  • The Pope

    July 10, 2009: President Barack Obama and First Lady Michelle Obama meet with Pope Benedict XVI at the Vatican on July 10, 2009. (Official White House photo by Pete Souza)

  • Punch

    July 13, 2009: President Barack Obama feigns a punch while talking about health care reform with Nancy-Ann DeParle, Peter Orszag, Phil Schiliro and Larry Summers in the Outer Oval Office, July 13, 2009. (Official White House Photo by Pete Souza)

  • Teasing

    June 26, 2009: President Barack Obama jokingly reacts to news that staffer Nora Becker will be leaving to pursue a joint MD and PhD in healthcare economics, during the White House staff picnic on the South Lawn, June 26, 2009. (Official White House Photo by Pete Souza)

  • Nancy Reagan

    June 2, 2009: President Barack Obama and former First Lady Nancy Reagan walk side-by-side through Center Hall in the White House, June 2, 2009. To the left of Mrs. Reagan hangs her official White House portrait as First Lady. (Official White House Photo by Pete Souza)

  • Cairo Visit

    June 4, 2009: Secretary of State Hillary Clinton recounts a story to President Barack Obama, Senior Advisors David Axelrod and Valerie Jarrett, outside the Sultan Hassan Mosque in Cairo, Egypt, June 4, 2009. (Official White House Photo by Pete Souza)

  • The Sphinx

    June 4, 2009: President Barack Obama tours the Egypt's Great Sphinx of Giza (left) and the Pyramid of Khafre, June 4, 2009. (Official White House photo by Pete Souza)

  • Behind The Camera

    Feb. 18, 2009: President Barack Obama takes aim with a photographer's camera backstage prior to remarks about providing mortgage payment relief for responsible homeowners at Dobson High School, Mesa, Ariz., Feb. 18, 2009. (Official White House Photo by Pete Souza)

  • First Day

    Jan. 21, 2009: President Barack Obama walks into the Oval Office for his first full day in office, Jan. 21, 2009. His Personal Aide Reggie Love stands nearby. (Official White House photo by Pete Souza)

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