FORT LAUDERDALE, Fla. (AP) — Florida begins in-person early voting in much of the state Monday as the Trump campaign tries to cut into an early advantage Democrats have posted in mail-in votes in the key swing state.

With its 29 electoral votes, Florida is crucial to both candidates but especially so for President Donald Trump, who moved his official residence to his Palm Beach estate Mar-a-Lago from New York last year. A Florida loss would make it nearly impossible for Trump to reach the 270 electoral votes needed to retain the White House over former Democratic Vice President Joe Biden.

Under state law, counties can offer up to two weeks of early voting and many do, including Miami-Dade, Broward, Palm Beach and other population centers. Large counties offer multiple sites and all counties allow those who have received mail-in ballots to drop them off. The latest a county can start early voting is Saturday.

About 2.5 million mail-in ballots have already been cast, with Democrats returning 1.2 million and Republicans about 755,000 as of Sunday. Non-affiliated voters and third-party members make up the rest. The number of mail-in votes is already approaching the 2.7 million cast in 2016 when Republicans had a 70,000-vote margin on returns. Trump defeated Hillary Clinton in the state by about 113,000 votes. No Republican has won the presidency without winning Florida since Calvin Coolidge in 1924.

Florida Republicans have said they aren’t worried about the mail-in gap, believing any advantage Biden gets will be swamped by Trump supporters casting in-person ballots starting this week and on Election Day. They believe Democrats are “cannibalizing” their own votes — moving in-person voters to mail-in without increasing their overall support. They point to their increased voter registration, which narrowed the Democrats' lead to 134,000, down 327,000 four years ago.

Long lines have plagued early voting sites in Georgia and other states, but Florida county elections supervisors have said they expect lines to move smoothly.

Some elections in Florida have been won on the thinnest of margins, becoming the center of intense focus during recounts of ballots — including the 2000 presidential race between Republican George W. Bush and Democrat Al Gore. The recount drew a chaotic slew of court challenges that ultimately ended with U.S. Supreme Court halting further recounting, deciding the race for Bush.

Elections officials are predicting that between mail-in ballots and early voting, about 70% of the ballots expected will be cast before Election Day. The state allows those ballots to be processed, but the actual count remains secret until after the polls close Nov. 3.

Counties must end early voting by Nov. 1. Mail-in ballots, with few exceptions, must be received by 7 p.m. Nov. 3.