When they go to the polls Aug. 20, Democratic primary voters in the Orlando area will decide the winner of one Florida Senate seat, while voters in other parts of the state will set the final slate of Senate candidates for the November elections.

The primary elections won’t affect the supermajority that Republicans hold in the Senate. But some Republican and Democratic primaries are drawing big money and big-name endorsements.

Voters have started casting mail-in ballots, and early-voting sites started opening in some areas of the state Monday — and will have to be open statewide on Saturday.

Here are five Senate primaries to watch:

SENATE DISTRICT 7: The Republican primary has drawn a flood of money and endorsements as House Appropriations Chairman Tom Leek, R-Ormond Beach, former St. Johns County Sheriff David Shoar and financial adviser Gerry James seek to represent the heavily Republican district.

Term-limited Sen. Travis Hutson, R-St. Augustine, cannot seek re-election in the district, which is made up of St. Johns, Putnam, Flagler and part of Volusia counties.

Leek has received endorsements from Gov. Ron DeSantis, U.S. Sen. Rick Scott, Attorney General Ashley Moody, state Chief Financial Officer Jimmy Patronis, incoming Senate President Ben Albritton, R-Wauchula, and House Speaker Paul Renner, R-Palm Coast.

But former President Donald Trump on Saturday endorsed Shoar, describing him as “100% MAGA.”

Money has poured into the race through webs of political committees, with many businesses and industry groups backing Leek and trial lawyers supporting Shoar.

The winner of the GOP primary will face Democrat George Anthony ‘T’ Hill II in November.

SENATE DISTRICT 13: With longtime Republican lawmaker Dennis Baxley facing term limits, Rep. Keith Truenow, R-Tavares, is going up against Bowen Kou and Cheryl “CJ” Blancett in the GOP primary in District 13, which is made up of Lake County and part of Orange County.

Kou, who built a chain of grocery stores and bakeries after immigrating to the U.S. from China, has faced attacks during the campaign from the Florida Republican Senatorial Campaign Committee, which is headed by Albritton and supports Truenow. Kou has sued over mailers and a TV ad that claimed he has ties to the Chinese Communist Party.

Truenow also has drawn the backing of DeSantis and other state GOP leaders. Kou has put about $1.14 million of his own money into the race, according to a state campaign-finance database. Blancett, a small-business owner, drew headlines when she was charged with stealing money from a homeowners association whose finances she managed.

The winner of the GOP primary will face Democrat Stephanie Dukes in November.

SENATE DISTRICT 15: Sen. Geraldine Thompson, a Democrat in her second stint in the Senate, faces a challenge from former Sen. Randolph Bracy, who left the Legislature and ran unsuccessfully for Congress in 2022.

Both are familiar faces in Tallahassee: With the exception of a two-year period, Thompson has served in the House or Senate since 2006; Bracy served four years in the House and six years in the Senate.

The contest in the Orange County district has become personal. Without a Republican candidate, the primary will be open to all voters and will decide who represents the district for the next four years.

Bracy’s mother was Thompson’s college roommate, and the families are well-known in the region. Meanwhile, questions have been raised during the campaign about Thompson’s residency in the district and Bracy’s finances.

“The District 15 race between Thompson and Bracy has also gotten heated with some Bracy relatives endorsing Thompson and Bracy under fire for incomplete financial disclosure forms that show he has a lot more money than he had a few years ago, but do not specifically show where that money came from,” University of Central Florida political-science professor Aubrey Jewett said.

Thompson has received assistance from the Florida Democratic Legislative Campaign Committee, which is headed by incoming Senate Minority Leader Jason Pizzo, D-Sunny Isles Beach.

SENATE DISTRICT 25: Republicans and Democrats will choose their nominees in the primaries in District 25, which is made up of Osceola County and part of Orange County and is open because Sen. Victor Torres, D-Orlando, faces term limits.

Democrats will choose between Rep. Kristen Arrington of Kissimmee, former U.S. Rep. Alan Grayson and Carmen Torres, who is married to Victor Torres. Grayson made a late entrance into the race in June and has loaned $103,000 to his campaign.

On the Republican side, Osceola County School Board member Jon Arguello is going up against Jose Martinez, a business owner.

The district leans Democratic.

SENATE DISTRICT 35: Three Democrats — Rodney Jacobs, Chad Klitzman and former Broward County Commissioner Barbara Sharief — are competing to replace term-limited Senate Minority Leader Lauren Book, D-Davie, in the Broward district.

Sharief has filed a lawsuit against Jacobs, alleging he defamed her in a campaign ad by implying she and her health-care company, South Florida Pediatric Homecare, defrauded Medicaid. Sharief unsuccessfully ran against Book in 2022 and filed a similar lawsuit against the senator.

Jacobs heads the Miami Civilian Investigative Panel, while Klitzman is an attorney and screenwriter.

The Democratic primary winner will be the favorite to win the seat in the November election against Republican Vincent Parlatore.