Tuesday’s primary punctuates just how much Florida, once the nation’s largest swing state, has been transformed into a solidly Republican bastion.

Florida’s electoral contests are no longer the nail-biters that led to past recounts and countless late-night jokes. Its politics now reflect how Republicans have consolidated power in President Trump’s adopted home state, which has become a proving ground for the next generation of ambitious Republican politicians.

On Tuesday, voters will choose congressional nominees under a map gerrymandered by Republican state lawmakers that added four new Republican-leaning seats. The map, part of a sweeping national battle that Democrats decried as a Republican power grab, may be the last major victory for Gov. Ron DeSantis, whose nearly eight years in office muscling through right-wing policies are drawing to a close because of term limits.

His would-be successors are also on the ballot, as are candidates vying to represent Florida in the Senate. Neither contest is as high profile as it would have been a decade ago.

The races may draw attention solely because Republicans are in a tough midterm election year, dragged down by Mr. Trump’s sagging poll numbers. And Democrats, who voted in abysmal numbers in Florida in the 2022 midterms, have some newfound energy after two special-election victories and progressive momentum across the country.

Still, Florida structurally favors Republicans, who hold every statewide elected office and supermajorities in both chambers of the Legislature. They have also drastically swung voter registration in the state: In 2018, registered Democrats outnumbered Republicans by about 250,000 voters. Today, Republicans outnumber Democrats by more than 1.5 million voters.

“We’ve had a great run in Florida,” Mr. DeSantis said in June, highlighting the turnaround in registration numbers. “We’ve really respected the voters and worked really hard to build that trust and support.”

Florida had 13 Democrats in its congressional delegation as recently as six years ago. It could have as few as four as soon as next year, if the gerrymandered map goes entirely Republicans’ way.

So few potentially competitive districts remain in Florida that a majority of the state’s 28 congressional races will be all but settled in the primaries. Republicans appear most worried about the Seventh Congressional District, northeast of Orlando, where Representative Cory Mills is seeking re-election despite being bogged down by scandals. He has been accused of assault — though no charges resulted — and is under investigation by the House Ethics Committee.

Two fellow Republican lawmakers have endorsed one of his challengers, saying the party should not risk losing a seat by nominating Mr. Mills. Even Mr. DeSantis made a point of saying last week that Mr. Mills did not have his support.

The gerrymandered map eliminated the districts of two Democrats, Representatives Jared Moskowitz and Debbie Wasserman Schultz, both in South Florida. Mr. Moskowitz is running in the newly created 25th Congressional District, along coastal Palm Beach, Broward and Miami-Dade Counties. It is considered the only competitive open seat in the state.

What does “competitive” look like in today’s Florida? Mr. Trump won the district by nine percentage points in 2024.

To compete in the general election, Mr. Moskowitz, a two-term congressman, must first defeat Oliver Larkin, a democratic socialist, in the Democratic primary. Mr. Larkin is one of three democratic socialists on Tuesday’s ballot; they are trying to show that progressive policies would help Democrats regain a foothold in the state, despite its increasingly Republican lean and distaste for anything related to socialism.

“There’s a definite hurdle that we need to get over,” Mr. Larkin acknowledged in an interview, lamenting “a lot of fear-mongering about democratic socialism.” But, he added: “I think what we’ve seen is a real appetite for this kind of change within the Democratic Party.”

Ms. Wasserman Schultz, an 11-term incumbent, chose to compete in the 20th Congressional District, which is safely Democratic. It includes African American and Caribbean American communities in Broward County and has historically been held by a Black representative.

Ms. Wasserman Schultz is white, and her decision to run frustrated four Black Democrats who were already vying for the seat. But because they could not agree to back a single Black unity candidate, the four candidates may split the vote, paving the way for Ms. Wasserman Schultz to win.

After Tuesday, the 76-day campaign until Election Day will be dominated by the contests at the top of the ticket, which remain long shots for Democrats.

Senator Ashley Moody, a Republican, was appointed by Mr. DeSantis last year to the seat vacated by Marco Rubio when he became secretary of state. She is running to complete the remaining two years of Mr. Rubio’s term. Ms. Moody does not have any serious primary opposition, but she remains little known to many voters, despite having previously been elected to two terms as the state’s attorney general.

Though Democrats acknowledge that defeating Ms. Moody will be tough, they still consider their odds against an appointed senator to be better than they have been in several election cycles. The Democratic front-runner, Alex Vindman, a former National Security Council expert, was a witness against Mr. Trump in his first impeachment trial and has out-raised Ms. Moody as he tries to build a campaign apparatus from scratch.

First, Mr. Vindman faces off in the primary against State Representative Angie Nixon, a progressive firebrand who has waged an underdog campaign over the past year on issues such as establishing universal health care and abolishing Immigration and Customs Enforcement. She recently joined the Democratic Socialists of America. There has been little independent polling in the race.

As tends to be the case in Florida, the governor’s race may be the most intriguing going into November.

Two years ago, the open contest to succeed Mr. DeSantis looked as if it would feature a marquee lineup of every big-name Republican in the state. Mr. DeSantis expanded executive power and parlayed the national profile he gained during the Covid pandemic into a run for president in the 2024 primary. He had shown how big and influential the position could be.

Instead, a single Republican has dominated the race: Representative Byron Donalds of Naples, who received Mr. Trump’s endorsement in February 2025, before Mr. Donalds had even declared his candidacy. Mr. Donalds had backed Mr. Trump over Mr. DeSantis in 2024, and Mr. Trump returned the favor.

For months, Florida Republicans waited for Mr. DeSantis to pick an heir, assuming the race would come down to a Trump candidate and a DeSantis candidate. When Mr. DeSantis replaced his lieutenant governor last year with Jay Collins, who had been loyal to him while serving in the State Senate, it appeared that he was setting up Mr. Collins to run.

But Mr. Collins proved to be a disappointing fund-raiser and stump speaker. Mr. DeSantis considered having his wife, Casey, run, but she was marred by an investigation tied to her charity.

In the end, Mr. DeSantis endorsed no one, a shocking outcome for a governor who had used his considerable popularity to help elect Republicans up and down the ballot in past elections.

That has left Mr. Donalds, a strong fund-raiser who has built a statewide campaign organization, as the dominant candidate in the race. If elected, Mr. Donalds will be Florida’s first Black governor.

Speaking on Monday in Plant City, just outside Tampa, Mr. Donalds vowed to make life in Florida more affordable. He recalled his own days struggling to make ends meet as a young husband and father, saying he would work with state lawmakers to lower home insurance rates.

“We want to make sure that Florida dream is alive and well for everybody in our state,” he said.

Mr. Donalds is likely to face former Representative David Jolly as the Democratic nominee. Mr. Jolly, who was a Republican when he served in Congress, became an independent and then a Democrat last year. Over that time, he reached out to grass-roots Democrats to reassure them that he was now one of them — while running squarely as a moderate to try to win crossover Republican voters in the general election.

Mr. Donalds and his campaign supporters have already been attacking him in television ads and on the trail. On Monday, Mr. Donalds portrayed Mr. Jolly as a turncoat and noted that Democrats had already run a former Republican, Charlie Crist, in the last governor’s race — and lost in a rout.

“They didn’t learn their lesson,” Mr. Donalds said.

Mr. Jolly responded on social media. “After 30 years of one-party rule,” he wrote on X, “voters are ready for change.”

David Ovalle contributed reporting from Miami.