FORT LAUDERDALE, Fla. (AP) — Slightly more Florida Democrats have cast ballots than Republicans as the nation's largest swing state heads into Election Day, but that is a position they were in four years ago before President Donald Trump's late surge narrowly took the state.

With early voting completed and the return of mail-in ballots slowing, state figures released Monday show that out of 9 million ballots cast, 108,000 more Democrats have voted than Republicans. It is unknown who these voters cast ballots for, but Democrats are expected to overwhelmingly support former Vice President Joe Biden. The same applies to Republicans and Trump.

Florida, with 29 electoral votes, is a must-win state for Trump to have a realistic chance of being reelected. The pre-Election Day margin in the president's adopted home state was slightly tighter in 2016, when 96,000 more Democrats voted early or by mail than Republicans out of 6.5 million cast — but Trump had a strong turnout on Election Day and carried the state over former Secretary of State Hillary Clinton by 113,000 votes or 1.2 percentage points.

There is one significant difference this time — because more voters have already cast ballots, significantly fewer are expected to show up Tuesday. In 2016, 3 million Floridians voted on Election Day. This year, between 1.5 million and 2 million are expected, meaning Trump will need to carry a larger percentage of those.

There is also the question of how independent voters will split — they make up 2 million or about 22% of the votes cast so far. Some analysts think Biden has a slight edge because Florida independents tend to be younger than the average voter and the group also includes a significant contingent of Puerto Ricans, many arriving after 2017's Hurricane Maria. Both groups lean Democratic.

Mix it together and analysts say Florida is a state that is again too close to call. Four of five presidential elections in the 2000s have been decided by 3 percentage points or less, with the 2000 race ending in the infamous recount where Republican George W. Bush defeated Democrat Al Gore by 537 votes.

Democrats dominated the mail-in vote this year: 2.1 million returned ballots compared to 1.45 million for the Republicans. Republicans dominated the walk-in early voting: 1.9 million to 1.4 million.

Kevin Wagner, a political science professor at Florida Atlantic University, said some think the Democrats, because of the pandemic, turned a significant chunk of their early voters into mail voters, gaining little in the process. But, he said, Republicans might have turned a chunk of their Election Day voters into early voters: they would already be in the count and that would make a Tuesday comeback less possible.

Another factor that is impossible to gauge, is how large each party’s defection rate will be, said Wagner and Susan MacManus, a University of South Florida political science professor. If one side holds 95% of its voters, while the other only holds 90%, for example, that could be decisive.

Florida still has a pool of “Dixiecrats” — conservative Southern Democrats who began voting Republican with Ronald Reagan in the 1980s while never switching their registration. On the Republican side, there is a sizeable pool of “Never Trumpers,” conservatives who dislike the president and could support a Democrat like Biden.

Still, Wagner thinks Trump will eliminate the gap.

“My gut feeling is that Trump is going to pull (Florida) out by a hair, but I have nothing to back that up,” he said.

MacManus said because early and mail-in voting is so tight, winning Florida will again come down to which party gets voters to the polls on Tuesday. Historically, that has been the Republicans, but she has seen some signs Democrats could do better this time.

“Whoever has the best ground game will win,” she said.

Trump Florida spokeswoman Emma Vaughn said the campaign's “permanent, data-driven ground game cannot be matched by Joe Biden’s anemic efforts in the Sunshine State. We are right where we need to be and we will continue to get out the vote.”

Christian Ulvert, a senior Biden adviser in Florida, said the high turnout is a boon for Democrats, who had a larger percentage of their Florida voters sit out the 2016 election than Republicans. Former President Barack Obama's visit later Monday to Miami will help push additional Democratic voters to the polls in a key region, he said.

“Our turnout operation really went into overdrive this weekend,” he said.

Polls close at 7 p.m. Tuesday local time and mail-in ballots must be received by the voter's county by that hour to be counted.

Significant returns are expected to be released by 10 p.m. Tuesday as early votes and mail-in votes received through Monday will already be counted, that tally hidden inside computers until the polls close.