Early voting figures for the US presidential election suggest an increase in Republican turnout compared to 2008, while Democrats are celebrating an advantage among “sporadic” voters – those who do not vote regularly, and could mean the difference between victory and defeat in the tight presidential race.

Both Republicans and Democrats this week claimed early voting figures, which will likely amount to more than one-third of the total votes cast in the election, show the election leaning in their direction.

“We’re turning out voters who have been traditionally less likely to participate, sometimes called ‘sporadic’ voters…. Overall, we’re winning early vote in the battleground states that will decide this election — a key part of our plan to get to 270 electoral votes,” Jeremy Bird, the Obama campaign’s national field director, wrote in a Wednesday memo on the campaign’s website.

“With less than two weeks until Election Day, the unprecedented GOP ground game is producing dramatic results in absentee balloting and early voting (AB/EV) that will give us a critical edge,” Rick Wiley, political director of the Republican National Committee, wrote in a memo released to journalists, also on Wednesday.

“We will continue to build on this momentum in the next thirteen days, meaning it will be increasingly difficult for Democrats to cobble together the necessary votes,” Wiley promised.

The campaigns’ bluster reflects the growing importance of early voting, which has increased from 16 percent of total votes cast in the 2000 election to 22% in 2004 and 30.6% in 2008. Nearly seven million votes have already been cast in the 2012 race, with two weeks still remaining until Election Day.

Early voting is doubly important, because it helps to set the narrative in the crucial last days of the campaign. It is this narrative – Mitt Romney’s “momentum” against Barack Obama’s newfound energy – that the campaigns are trying to shape in discussing early voting figures.

According to the RNC’s Wiley, Republicans are showing greater interest in early voting than in years past, a clear sign that enthusiasm is higher on the Republicans’ side.

“The data show the percentage of AB/EV [absentee ballot/early vote] activity from Republicans is greater than the percentage of registered voters which are Republican, indicating higher turnout rates among registered Republicans than among registered Democrats. For example, Republicans are outperforming our share of voter registration in absentee requests and early votes by 5.6 points in Florida, 8.73 points in Ohio, and nearly 12 points in Pennsylvania,” all crucial swing states in this election.

Republicans are also more enthused in 2012 than they were during the failed Republican presidential campaign of 2008.

“In most cases, the data show Republicans making up a larger share of early voters this year than they did four years ago. Democrats make up a smaller share, giving Republicans an important advantage. Across the eight states, Democrats are underperforming their share of 2008 AB/EV votes cast by a net 5.85 percentage points, while Republicans are over-performing their share by 2.13 points, yielding a net swing of +7.98 percentage points for Republicans.”

Yet while Republican figures show more enthusiasm, Democrats are claiming both a numerical advantage in early voting and newfound interest among those who don’t usually pay close attention to politics, as evidenced by their “sporadic” voting patterns.

“When you look inside the numbers so far, among sporadic voters it’s not even close. More sporadic Obama voters are voting than sporadic Republicans in the battleground states,” according to the Obama campaign’s Bird.

“Across nine battleground states, Democrats have a 19.7 point advantage in ballots cast among non-midterm voters. More than half (51.5 percent) of non-midterm voters who have voted already are Democrats, while fewer than a third (just 31.8 percent) are Republicans,” Bird wrote.

Among all voters, “Democrats have a 10.7 point advantage over Republicans. Just under half (49.6 percent) of voters who have cast ballots are Democrats, while just 38.9 percent are Republicans. In the only two states – Colorado and Florida – where Republicans lead right now in total ballots cast, Democrats are cutting into traditional Republican leads there; we’re doing better today than at this point in 2008.”

Early voting is legal without restrictions in 31 US states, including crucial swing states like Florida, Ohio and Pennsylvania. Mail-in absentee ballots are available without restriction in 22 states. Both mechanisms are intended to prevent overcrowding on Election Day, when voters might decide to avoid long lines at polling booths, thereby forfeiting their opportunity to cast their ballot.

In the crucial swing state of Ohio, 800,000 had already voted by Tuesday, and another 900,000 had requested an absentee ballot, accounting for over 20% of Ohio’s 7.9 million registered voters, according to figures released by Ohio Secretary of State Jon Husted Wednesday.

Among swing states, over 925,000 have already voted in Florida, 250,000 in Virginia, 215,000 in Nevada and 800,000 in North Carolina.