Democrats are hoping for a long-shot victory in special elections being held on Tuesday in Florida’s First and Sixth Congressional Districts as they look to erode the G.O.P.’s narrow majority in the House.

The districts are heavily Republican: In November, President Trump won Florida’s First by a 37-point margin and the Sixth by 30 points.

But special elections tend to be better for Democrats, who have already achieved upsets in multiple state legislative special elections this year. In January, the Democratic candidate for a State Senate seat in Iowa won by four points in a district Mr. Trump had taken by 20 points. In March, a Pennsylvania Democrat won by two points in a special State Senate election in a district that Mr. Trump carried by more than 10 points last year.

Further raising Democrats’ hopes, some recent polls have found a tighter than expected race in the Sixth District.

We are tracking the partisan split of the voters who have cast ballots in both Florida special House races. While data on which voters have turned out can be useful for understanding which party has an advantage, it cannot conclusively tell us who will win. For one thing, Democratic or Republican voters may not necessarily vote for their party’s candidate. In addition, a significant share of the electorate is not registered with either party.

We’ve split turnout into two buckets: “early turnout,” which encompasses voters who returned a mail ballot and those who voted early in person, and “Election Day turnout,” which will populate on Tuesday as people vote in person. First polls will close on Tuesday at 7 p.m. Eastern.

Note that partisanship can substantially differ between people who vote in person on Election Day and those who vote early. In general, voters who cast ballots early, particularly those who vote by mail, tend to be more Democratic than people who vote in person on Election Day.

For context, our tracker also includes turnout and the results of the presidential election in these districts from the 2024 presidential election for early and Election Day voters.

Florida’s First Congressional District was previously represented by Matt Gaetz, who resigned just days after being re-elected after he was nominated by Mr. Trump to be attorney general. Mr. Gaetz eventually withdrew himself from consideration. The Democrat Gay Valimont and the Republican Jimmy Patronis are on the ballot.

Florida’s Sixth Congressional District was vacated by Michael Waltz after President Trump selected him to be his national security adviser. Mr. Waltz recently included an Atlantic editor in a Signal group chat in which top U.S. officials discussed sensitive military plans. Joshua Weil, a Democrat, and the Republican Randy Fine are running for his old seat.

Jonah Smith contributed data analysis.