The Herald analysis shows that about 300,000 voters who signed up since the spring cast early ballots. Democrats say they’re beating Republicans when it comes to the number of first-time voters and voters who cast a ballot just once in the past three elections. But Republicans hold an edge when it comes to long-time reliable voters who have cast ballots — their base.

A big unknown: independent voters, who lean in Romney’s favor, according to most Florida polls. An unscientific Miami Herald email survey of more than 2,000 non-partisan voters who cast absentee ballots, however, found Obama winning the independent vote.

Because Florida is so close, independents essentially cast the tie-breaker. About 806,000 independents have already voted — about 18 percent of early ballots.

Overall, Democrats are ahead of Republicans 43-39 percent in early ballots cast. But the margin was much larger in 2008, when Democrats had a cumulative lead of as much as 363,000 ballots in 2008, or about 8 percentage points, according to data maintained by George Mason University. Using a different set of figures, Democrats say their lead was about 269,000. Republicans say it was about 315,000.

“President Obama built his campaign around the word ‘forward,’ but his ground game went in reverse. Early voting and absentee ballot voting is down in key Democratic strongholds like Miami-Dade County. Statewide, early and absentee voting among Democrats is down 50 percent from 2008,” said Alberto Martinez, a Romney campaign advisor from Florida, noting the relatively solid position Romney has in the polls.

Although registered Florida Democrats outnumber Republicans by 4.5 percentage points, the GOP frequently turns out a higher proportion of its voters, Martinez notes. “Our voters are ready to go to the polls even if it rains fire,” he said.

But Ashley Walker, the Obama campaign’s Florida chief, said Republicans are just offering “spin” because they don’t have the numbers. She acknowledges Obama has had a tougher campaign in 2008, but he’s ahead.

“I’d rather be on the plus-side rather than being in the position Romney’s campaign is in,” Walker said. “We’re basically banking votes. We just have to organize tomorrow and make sure folks turn out and finish off the half.”

Weighing on Obama: the bad economy. Also, the GOP-led Legislature and Republican Gov. Rick Scott cut early voting days to eight from 14. The early voting hours in South Florida were 20 percent lower this year compared to 2008.

In comparison to 2008, in-person early voting in Miami-Dade is down 27 percent. But Democrats increased their margins with absentee ballots to make up some of the difference.

Polls indicate that Obama needs an outsized turnout in urban Southeast Florida to shield him from heavy losses in rural North Florida.

Statewide, early-vote ballots are down about 200,000 compared to 2008, while absentee votes are up about 300,000.

To meet some of the demand of early voters, South Florida elections supervisors allowed voters to pick up absentee ballots and vote them in-person at each election office headquarters on Sunday — a day specifically barred from offering early voting under the election law Scott signed in 2011.

On Monday, Skye Barth stood in a line of about 250 people shortly before noon at Miami-Dade’s election headquarters in Doral. A student, she borrowed a car Monday morning, on her day off, to make it because she didn’t think she would make it to her precinct Tuesday.

“Today’s the last chance,” said Barth, 30. “You have do what you have to do.”

Starting at 7 a.m., the campaign that has more voters like Barth will likely walk away the winner.

Miami Herald staff writer Patricia Mazzei contributed to this report.