President Obama and Mitt Romney are tied in the critical battleground state of Ohio, according to the latest Suffolk University poll, but Obama has a significant lead over his GOP challenger among those who have already voted.

Obama and Romney each took 47 percent support in the poll of likely voters. That’s nearly in line with the RealClearPolitics average of polls, which shows Obama ahead by 1.9 percentage points in the state.


However, Obama has a massive 54 to 41 lead over Romney among those who said they have already voted. The president also leads among those who say they plan to vote before Election Day, 48 to 44, while Romney leads among those who say they will vote on Election Day, 49 to 44.

A survey from Democratic-affiliated Public Policy Polling (PPP) released Saturday similarly shows a tight race, with Obama topping Romney 49-48. A CBS News/Quinnipiac poll released Monday shows Romney with a late surge in the state, but Obama holding a 5-point lead with 50 percent support to 45.

Ohio is lining up to be a toss-up state with a high likelihood of swinging the election. It's especially important for Romney, who is generally considered to have a narrower path to victory through the Electoral College. No Republican has ever lost Ohio and gone on to win the presidency.

The Obama campaign has made early voting central to its get-out-the-vote efforts. The president will cast his ballot early this week in Illinois.

Last week, the Obama campaign circulated a memo claiming to be well ahead of Romney among early voters in the Buckeye State.

“Today we are ahead of where we were at this time against John McCainJohn Sidney McCainCNN's Ana Navarro to host Biden roundtable on making 'Trump a one-term president' Mark Kelly clinches Democratic Senate nod in Arizona Prominent conservatives question Jerry Falwell Jr. vacation photo MORE — and ahead of Mitt Romney,” national field director Jeremy Bird wrote. “Republicans are similarly talking up their ground game and early vote numbers, but their assertions rest on much shakier ground.”

The Bird memo pointed to four polls that show Obama with leads of between 19 and 52 points in Ohio among early voters, and argued the demographics and geography of those who had voted early strongly favors the president.

The Republican National Committee responded by calling the Obama campaign memo “panicked,” and argued that Republicans have been shrinking the president’s lead in Ohio early voting.

 “Their 20 point advantage in 2008 is now less than 7 and shrinking,” said GOP communications and research director Tim Miller in an email.

Republicans have also argued that early voting merely cannibalizes a candidate’s Election Day turnout.

Early voting has been a controversial issue in this election cycle, as Ohio's laws faced legal challenges. Last week, the Supreme Court said early voting in Ohio could continue, a ruling viewed as a major victory for the president.

Democrats initiated the legal battle over Ohio's early voting policy after state officials decided to eliminate three days of early voting that were offered in 2008. Minorities, who traditionally favor Democrats, often take advantage of early voting.