President Obama and Mitt Romney are neck-and-neck in national polls released on the final weekend before Election Day, but Obama's Midwestern "firewall" of Iowa, Ohio and Wisconsin is holding and he maintains a distinct advantage in the contest for the 270 electoral votes needed to win the White House.
The disparity between the national and state surveys presents two potential scenarios for Tuesday night: The two will converge, with Obama edging up in the national popular vote or Romney surging in battleground states, or Obama could become the second candidate in the last four elections to win the Electoral College and the presidency while capturing fewer votes than his opponent.
The national polling all suggests a tight race. The latest ABC News/Washington Post tracking poll shows the candidates tied with 48 percent of the vote, as does a new Politico-George Washington University Battleground poll. The final NBC News/Wall Street Journal poll of the campaign, slated for full release Sunday night, shows Obama with a 1-point advantage, 48 percent to 47 percent, well within the margin of error.
The last poll from the Pew Research Center, released Sunday afternoon, swung toward Obama, giving the incumbent a slight lead, 48 percent to 45 percent. The week before, the candidates were tied, and Obama has turned around what was a 4-point deficit after the first presidential debate.
Still, the balance of the national polling shows a tied race. Those numbers largely stand in contrast to the battleground-state polling, which shows Obama with a small but perceptible advantage. He's ahead in new polls of Iowa and Ohio, while the polls diverge in Florida and show a tightening race in New Hampshire.
In Iowa, Obama leads in the race for the state's six electoral votes, 47 percent to 42 percent, according to a Des Moines Register poll published in Sunday's editions. The poll shows Romney with a 3-point edge among men, while Obama leads by 12 points among women. More than two in five likely voters, 42 percent, have already voted, the poll found.
Reliable polling from Ohio continues to show Obama with a slight, discernible edge. A CNN/ORC poll released late on Friday had Obama with a 3-point lead, compared to an NBC News/Wall Street Journal/Marist poll that had Obama ahead by 6 points. On Sunday, the Columbus Dispatch released the results of its latest mail survey, which showed Obama ahead by 2 points, 50 percent to 48 percent. (Though mail is considered an outdated survey technique, it was once the most common method for polling, and the Dispatch's results have historically been accurate.)
This weekend's polls in Florida deliver a split decision: Obama holds a statistically insignificant 2-point lead in a new NBC News/Wall Street Journal/Marist poll, while a Mason-Dixon poll conducted for the Miami Herald, Tampa Bay Times and other media outlets in the state shows Romney ahead by 6 points. Florida is considered more essential to Romney's chances than Obama's, but a late advertising push from the Obama campaign shows the Democrats have not given up on the vote-rich state.
The race has tightened in New Hampshire, according to a new WMUR-TV Granite State Poll, which shows Obama and Romney tied at 47 percent apiece. Two weeks ago, Obama held an 8-point lead in a separate survey also conducted by the University of New Hampshire Survey Center.
Pennsylvania represents an interesting case, with two polls this weekend showing a tight race. A Muhlenberg College poll conducted for the Morning Call of Allentown shows Obama ahead by 3 percentage points, 49 percent to 46 percent. Meanwhile, Obama and Romney are tied in a new poll conducted by the Republican pollster Susquehanna Research and Polling for the Pittsburgh Tribune Review, each with 47 percent. But that actually represents an improvement for Obama: The previous Susquehanna poll, conducted in mid-October for the Pennsylvania GOP state committee, showed Romney leading by 4 points; Susquehanna is the only pollster to show Romney ahead in the Keystone State in the past few months.
There are some battleground states in which no new reliable, independent, live-caller polls were released this weekend. Polls over the last week have showed the race is neck-and-neck in Colorado, North Carolina and Virginia (an NBC News/Wall Street Journal/Marist poll in that state scheduled for release early on Monday will show a dead heat in Virginia), while Obama is leading in Michigan, Minnesota, Nevada and Wisconsin.
The electoral math still favors Obama. If Michigan, Minnesota, Nevada and Wisconsin are added to the list of states safely in his camp, he is at 233 electoral votes. Add Iowa, Ohio and Pennsylvania to that list, and he could afford to lose Colorado, Florida, New Hampshire, North Carolina and Virginia, where the polls are roughly tied. In that scenario, Obama would still win with 277 electoral votes.
Republicans insist that the public polls are wrong, suggesting that pollsters are making assumptions about the electorate that more-or-less replicate the voters who cast ballots in 2008 and claiming that too many Democrats are being interviewed. But, in most cases, public pollsters make no assumptions. They interview a randomly selected group of voters -- either by randomly dialing phone numbers or selecting random names off voter lists. They make sure they start with a demographically representative sample, but few pollsters make adjustments to that sample to match historical trends with respect to party identification.
It is certainly possible that the polls are less accurate than they have been in the past. Achieving a true random sample of Americans by telephone is harder -- and more expensive -- than ever. In order for Romney to emerge as a winner in the Electoral College, it appears that these polls will have to be proven not just inaccurate but biased toward the incumbent.