By STEPHEN OHLEMACHER
WASHINGTON (AP) - President Barack Obama heads toward Election Day with an apparent lead over Republican Mitt Romney among early voters in key states that could decide the election.
Obama's advantage, however, isn't as big as the one he had over John McCain four years ago, giving Romney's campaign hope that the former Massachusetts governor can erase the gap when people vote on Tuesday.
More than 27 million people already have voted in 34 states and the District of Columbia. No votes will be counted until Election Day but several battleground states are releasing the party affiliation of people who have voted early.
So far, Democratic voters outnumber Republicans in Florida, Iowa, Nevada, North Carolina and Ohio _ five states that could decide the election, if they voted the same way. Republicans have the edge in Colorado, which Obama won in 2008.
Obama dominated early voting in 2008, building up such big leads in Colorado, Florida, Iowa and North Carolina that he won each state despite losing the Election Day vote, according to voting data compiled by The Associated Press.
"In 2008, the McCain campaign didn't have any mobilization in place to really do early voting," said Michael McDonald, an early voting expert at George Mason University who tallies voting statistics for the United States Elections Project. "This time around the Romney campaign is not making the same mistake as the McCain campaign did."
McDonald said he sees a shift toward Republicans among early voters, which could make a difference in North Carolina, which Obama won by the slimmest of margins in 2008, only 14,000 votes. The Republican shift, however, might not be enough to wipe out Obama's advantage in Iowa and Nevada, which Obama won more comfortably in 2008.
In Colorado, Florida and Ohio, get ready for a long night of vote counting on Tuesday.
Romney's campaign aides say they are doing so much better than McCain did four years ago that Romney is in great shape to overtake Obama in many of the most competitive states.
"They are underperforming what their 2008 numbers were and we are overperforming where we were in 2008," said Rich Beeson, Romney's political director. "We feel very good heading into the Tuesday election."
Obama's campaign counters that Romney can't win the presidency simply by doing better than McCain.
"It's not about whether or not they're doing better than John McCain did," said Jeremy Bird, Obama's national field director. "It's about whether or not they're doing better than us."
About 35 percent of voters are expected to cast ballots before Tuesday, either by mail or in person.
Voters always can cross party lines when they vote for any office, and there are enough independent voters in many states to swing the election, if enough of them vote the same way. Still, both campaigns are following the early voting numbers closely, using them to gauge their progress and plan their Election Day strategies.
A look at early voting in the tightest states:
About 1.6 million people have voted, and Republicans outnumber Democrats 37 percent to 35 percent. Those numbers are a reversal from four years ago at this time. Inevitably, Obama won the early vote by 9 percentage points in 2008, giving him a big enough cushion to win the state, despite narrowly losing the Election Day vote.
Early voting in Colorado is expected to account for about 80 percent of all votes cast, giving it more weight than in other states.
About 3.9 million people have voted, and 43 percent were Democrats and 40 percent were Republicans. For years ago at this time, Democratic early voters had a 9 percentage point lead over Republicans.
Obama won Florida's early vote by 10 percentage points in 2008, getting 400,000 more early votes than McCain, enough to offset McCain's advantage on Election Day.
In Florida, Republicans have historically done better among people who vote by mail, while Democrats have done better among people who vote early in person. For 2012, Florida's Republican-led Legislature reduced the number of in-person early voting days from 14 to eight.
The Obama campaign responded by encouraging more supporters to vote by mail, and Democrats were able to narrow the gap among mail ballots. Democrats quickly took the lead among all early voters, once in-person early voting started. But the margins are slim.
The Obama campaign acknowledges it must do better among Florida's Election Day voters than Obama did on 2008, when McCain won the Election Day vote by 5 percentage points.