No one doubts that a record number of Americans have signed up to vote in Tuesday's presidential election — but just how big will the record be? The latest figures show that more than 184 million potential voters have registered, which could represent four out of five Americans older than 18.
If those statistics hold up, the percentages as well as the raw figures would exceed any level seen over the past four decades — and set the stage for what will be the biggest flood of ballots the nation has ever seen.
"The magnitude is a big point this time," Rick Hasen, a professor at Loyola Law School in Los Angeles who specializes in election law, told msnbc.com. "I think people agree that this is an important election."
However, the figures come with a lot of asterisks and caveats, particularly when it comes to guessing how many people will show up on Election Day.
The tally of registered voters is based on reports from election officials for 48 states, provided to msnbc.com by the National Association of Secretaries of State, with the addition of figures from Hawaii. North Dakota is left out of the calculations because that state doesn't register voters in advance.
The association's total comes to 184,213,797. Late Friday, The Associated Press released its own tally, which came up with a higher figure: 187,332,357. AP said that represented a 7.3 percent increase over closing registration figures from two years ago.
Figures from the 28 states that had party registration in 2006 and 2008 indicated that the Democrats have gained the most from that growth: Democratic registration increased 12.2 percent over the past two years, while GOP registration rose just 1.7 percent, AP said.
Running the numbers
If you plug in the current figures for estimated U.S. population (305 million) plus past figures from the U.S. Census Bureau about the proportion of that population older than 18 (75.5 percent), you might conclude that roughly 80 percent of the country's voting-age population has registered.
That would be higher than any voter registration rate reported since the Census Bureau started reporting such figures more than 40 years ago. In fact, the bureau's current high mark came exactly 40 years ago: For the 1968 presidential contest between Richard Nixon and Hubert Humphrey, the bureau estimated that registered voters made up 74.3 percent of the United States' voting-age population.
Unfortunately, making sense of the raw registration figures isn't that simple, said Michael McDonald, a professor at George Mason University who heads the United States Election Project. "We really can't assess this very well," he told msnbc.com.
He said the official registration records were almost certainly inflated — and not just because of the widely publicized cases of bogus "Mickey Mouse" voters. "What we have here is a situation where people may be re-registering, and there hasn't been enough time to purge the rolls," McDonald said.
Indeed, revised figures from California reduced the total reported by the National Association of Secretaries of States by about 4 million votes between Thursday and Friday.
The fact that the figures have been in flux is one of the reasons why Curtis Gans, director of the American University's Center for Study of the American Electorate, was waiting until Monday to issue his report on voter registration.
"It'll be a record number because our population has grown," he said. "Whether it'll be a record percentage is still waiting to be seen."
What will Election Day look like?
The key question has to do with how many of those registered voters show up at the polls on Tuesday. Compared with past years, absentee and early-voting levels have been "off the charts," McDonald said. Early voters have experienced long lines and hours-long waits at polling places across the country.
AP reported on Thursday that early votes and absentee votes have amounted to more than 18.5 million, based on reports gathered over the past week. Millions of additional early votes are expected to be added over the next few days. In comparison, the absentee/early vote total for the 2004 election was 24.6 million.
Some states have already logged more than twice as many pre-Election Day votes as they did in 2004. Ohio, which was a controversial battleground state in 2004 and may be again in this year's contest, leads the list with a 134 percent increase.
All this has led many observers to predict record turnout this year. But here come those caveats again: Although the rise in voter registration leaves little doubt that record numbers will go to the polls on Tuesday, the turnout percentage may or may not exceed the milestones seen in 1960 (Kennedy vs. Nixon, 64 percent) or 1908 (Taft vs. Bryan, 66 percent).
The dramatic rise in absentee and early votes could be the harbinger of a mammoth get-out-the-vote effort on Tuesday, or it could simply represent "people who are voting now who would have voted on Election Day" in past years, said Doug Chapin, director of Electionline.org at the Pew Center on the States.
"We honestly won't know which one of those is true until Election Day," Chapin said.
This report was updated on Oct. 31 to reflect revised numbers from the National Association of Secretaries of State.