Election Day could already be half over in Florida before polling stations open at 7 a.m.

More than 4.5 million people have voted early, which accounts for 38 percent of the state’s 12 million registered voters and half of the ones likely to cast a ballot.

Democrats have a lead in total ballots cast over Republicans — 167,000 — but polls indicate Republican Mitt Romney is in a better position than President Barack Obama.

Obama is worse off than he was four years ago. Depending on how the data are sliced, his pre-Election Day lead could be half of what it was in 2008.

Still, Democrats are up in early ballots.

“It’s half-over, but it’s tied,” said Michael McDonald, a George Mason University political science professor and early voting expert. “There’s still another half to play.”

This is the tough half. If Obama wins Florida, he wins re-election.

The campaigns will be phoning voters who don’t show up, providing rides and keeping electronic tabs on bellwether precincts. It’s a massive numbers game involving tens of thousands of grassroots volunteers and data-mining techies monitoring the campaigns’ progress — or lack thereof — in real time from headquarters in Chicago (Obama) and Boston (Romney).

McDonald said this Florida election had a surprise: Higher proportions of Republicans cast in-person early votes compared to 2008, and even higher percentages of Democrats cast absentee ballots, which are typically mailed.

About 2.1 million absentee ballots were cast statewide — in addition to 2.4 million in-person early votes. The numbers show that, when it comes to voting, Florida has racial divisions that play to each campaign’s strengths, according to an analysis of preliminary voter data conducted by The Miami Herald and the Florida Center for Investigative Reporting:

African-American voters: Accounting for less than 14 percent of the electorate, they prefer to vote in person rather than by mail.

Black voters have cast more than a quarter of the state’s early votes, but only about 9 percent of absentee ballots. About 90 percent of the African-American ballots are from Democrats.

Hispanic voters: More than 14 percent of the electorate, Hispanic voters appear to still prefer to vote on Election Day.

Hispanics cast about 12 percent of in-person early votes, with Democrats far outnumbering Republicans. The Democrats’ strength: Central Florida, home to liberal-leaning Puerto Ricans, where Democrats outvoted the GOP nearly 2:1.

But it’s a different story when it comes to absentee ballots, thanks to strong Cuban-American support in Southeast Florida, where Hispanic GOP absentee ballots were more than double those cast by Hispanic Democrats. Still, Hispanic Democrats cling to a narrow 37-41 percent lead over Republicans in the overall early vote. And Democrats have more Hispanics to turn out relative to the number of Republican Hispanics who haven’t yet voted.

Non-Hispanic white voters: About 67 percent of the electorate, white voters turn out in higher proportions than minorities during Florida elections. They cast 77 percent of absentee ballots, but only 61 percent of in-person early votes.

Obama needs an outsized minority turnout to counterbalance the disproportionate white vote that Romney is winning in polls. Obama also needs to rely on young and first-time voters. So the Obama campaign bolstered Democratic ranks by more than 320,000, many of them minorities, thanks to a mammoth voter-registration drive.