Sen. Marco Rubio, left, and former Florida governor Jeb Bush both lag behind Donald Trump and Ben Carson in Florida Republican presidential polling. (AP File Photos)

There’s fresh evidence here of the unthinkable: Florida’s biggest Republican stars, former governor Jeb Bush and Sen. Marco Rubio, run the risk of losing their state’s winner-take-all primary next year to an out-of-state contender.

A loss in their home state could force both out of the presidential race after March 15, when Florida and three other states will hold the first winner-take-all primaries.

The contests will come after New Hampshire, Iowa, Nevada and a slate of Southern states reward delegates proportionally — probably giving a good number of candidates enough support to keep going. But when Florida votes, the state will award all of its 99 delegates to the winner — enough support to potentially allow the victor to take a commanding lead.

Bush, Rubio and others in the GOP presidential field spoke Friday at the “Sunshine Summit,” a first-of-its kind conference for state Republicans.

Attending a kickoff dinner on Thursday night, Rubio warned that “a bunch of candidates” would be asking for votes.

Rubio and Trump shake hands as Bush looks on during the Republican presidential debate on Nov. 10 in Milwaukee. (Morry Gash/AP)

“One out of six Republicans is running for president,” he joked.

Unlike the early primary states, whose voters demand intimate retail-style campaigning, Florida has 10 television markets and encompasses disparate regions — including glitzy Miami Beach, the choked highways of Tampa and Orlando and the hardwood forests of the Panhandle. Campaigning here requires millions of dollars and an ability to woo a broad cross-section of the Republican Party — seniors in large retirement communities, active and retired military service members in the northeast, suburban families in Central Florida and Cuban Americans in Miami.

Bush won statewide elections in 1998 and 2002, while Rubio scored a come-from-behind victory in his 2010 Senate race. But neither is close to leading here in the Republican presidential race.

A poll released last week showed businessman Donald Trump with 37 percent of support among GOP voters; retired neurosurgeon Ben Carson had 17 percent. Rubio placed third, with 16 percent, followed by Sen. Ted Cruz (Tex.) at 10 percent. Bush earned 7 percent in the poll, conducted by SurveyUSA and Tampa-area television stations.

Part of the draw to the conference in Orlando this weekend is that the state party rewrote its ballot eligibility rules to encourage candidate attendance. Instead of collecting signatures or paying a five-figure fee to get on the ballot, candidates had the option of addressing the conference.

“Florida is definitely in play, and the winner-take-all aspect of it makes it that much more attractive,” said Brian Ballard, a longtime state GOP operative who recently switched allegiances from Bush to Rubio. “If someone who’s not a Floridian wins Florida, it’ll be a big delegate boost and a very big statement.”

Then-Rep. Marco Rubio holds a sword presented to him by then-Gov. Jeb Bush during ceremonies designating him as the state’s House speaker in 2005. (PHIL COALE/AP)

Susan MacManus, a professor of political science at the University of South Florida at Tampa and a longtime state political observer, said an out-of-state Republican could easily win the primary “if Bush and Rubio split the vote. The more candidates still in the mix by March 15, the more likely an outsider could get a plurality.”

But former Republican Sen. Mel Martinez, who supports Bush, warned that “it’s very expensive” to campaign in the state. By the time the presidential campaign gets to the Sunshine State next year, he said that “someone had better have the resources to compete in Florida — otherwise stay home.”

Initially, Trump, Carson and other out-of-staters paid little attention to Florida, assuming that Bush and Rubio would fight it out while everyone else competed in other winner-take-all contests being held that night in Illinois, Missouri and Ohio. But as Bush struggles to maintain support and Rubio only now begins to build it, their rivals sense vulnerabilities.

“The people of Florida like me, and I love them,” Trump said in a brief interview this week. “We’re doing really well in Florida, I’m leading Jeb and Marco, and I’m there a lot. I have a lot of property there. I employ thousands of people in Florida — thousands!”

Barry Bennett, campaign manager for Carson, said his team is “rethinking” its initial plan to skip Florida partly because “everybody is looking for a new, fresh face.”

Bennett pointed to Sen. Lindsey O. Graham (S.C.), Gov. John Kasich (Ohio) and Gov. Bobby Jindal (La.), none of whom is even close to winning his own state in the polls. Graham spoke at the Orlando conference on Friday, while Kasich, Jindal and Sen. Rand Paul (Ky.), who hopes to keep attention on a fight he had with Rubio during Tuesday night’s televised debate over taxes and increased defense spending, were to speak Saturday.

While in Orlando, Cruz announced members of his state leadership team and hold a campaign event.

Bush and Rubio have far superior campaign operations and the support of local politicians who can help mobilize voters.

Bush already has seven paid staffers or consultants working in two field offices in Miami and Tampa. He has held dozens of fundraisers and nearly 20 campaign events across the state. The closely watched relaunch of his struggling campaign began last week with quick stops in Tampa, Orlando and Jacksonville.

“Once the race gets to Florida, we’re confident Jeb’s proven conservative record of making a difference as governor and our team on the ground will allow us to be successful here,” said campaign spokeswoman Allie Brandenburger.

Eleven of the state’s 17 Republican congressmen support Bush, as do three statewide officeholders. All but two recent Republican speakers of the Florida House of Representatives support Bush.

Rubio — also a former Florida House speaker — does not have a field office in Florida; his national campaign is based in Washington. He has paid staffers organizing in the state, but aides declined to say how many. The campaign will soon announce a list of chairmen for each of the state’s 67 counties, according to a spokesman.

“It’s a big and diverse state, and I think it shows organizational strength,” said Rubio spokesman Alex Conant.

Miami-Dade County Republican Party Chairman Nelson Diaz said there’s a distinct difference between the way the Rubio and Bush campaign in the state.

“Marco’s campaign sort of takes advantage of an existing event and an existing crowd, whereas Jeb likes to do his own events and get his own people there,” said Diaz, a former Rubio aide who is neutral in the 2016 race because of his party role.

Trump has donated more than $100,000 to the political committee of Florida Gov. Rick Scott. The governor remains neutral in the race, but Trump enlisted his former campaign manager, Susie Wiles, to serve as a co-chair of his Florida campaign.

MacManus said that any Republican aspirant will have to spend “at least a couple million dollars” on advertising, especially since the state is home to the Miami, Orlando and Tampa media markets.

But Ballard said that momentum will matter much more. In addition to backing Rubio and previously supporting Bush, he is a Tallahassee-based lobbyist who handles state issues for Trump.

“Florida is always determined very late,” Ballard said. “What happens in South Carolina and New Hampshire matters a lot with what happens in Florida.”

Sullivan reported from Washington. David Weigel and Katie Zezima in Washington contributed to this report.