Supporters of Republican presidential candidate Donald Trump cheer during a campaign rally, Oct. 24, 2016, in Tampa, Fla.
Supporters of Republican presidential candidate Donald Trump cheer during a campaign rally, Oct. 24, 2016, in Tampa, Fla.

With Election Day two weeks away, Republican Donald Trump and Democrat Hillary Clinton campaigned Tuesday in Florida, a key state that is pivotal for both candidates seeking the U.S. presidency.

Florida, in the southeastern U.S., is the largest of the battleground states — those closely contested by the two main candidates — with the winner set to gain 29 electoral votes, more than 10 percent of the total necessary to win the White House.

The United States elects its presidents every four years through the Electoral College, with the most populous states having the biggest influence on the overall outcome, rather than the national popular vote. A simple majority of 270 electoral votes is needed to win.

Surveys in Florida show Clinton, a former U.S. secretary of state looking to become the country's first female president, ahead of Trump by about 4 percentage points. About 1.6 million of Florida voters have cast ballots, either in person at polling stations set up for advance voting or via absentee ballots.

Republican presidential candidate Donald Trump pos
Republican presidential candidate Donald Trump poses for photographs during an campaign event with employees at Trump National Doral, Tuesday, Oct. 25, 2016, in Miami.

Trump mocks 'phony polls'

Trump, the real-estate mogul who maintains an oceanfront mansion in Florida as his second home, said it is "probably true" that he cannot become the country's 45th president without winning Florida.

Public-opinion surveys show he is trailing Clinton by about 5 percentage points across the country; Trump has also fallen behind Clinton in other competitive states — the ones that are closely contested, year after year, by the Republican and Democratic parties.

"I believe Florida is must-win," Trump told Fox News. "I think we're winning it, think we're winning it big."

Trump is visiting seven cities in Florida over three days, telling voters he is ahead, and mocking the surveys he calls "phony polls" that say the opposite. He contends the national media have joined with the Clinton campaign to create a "rigged election," although he has not offered any evidence or specifics of how that could happen.

WATCH: Trump on Obamacare, rigged system

On Tuesday, he told a crowd that President Barack Obama's national health-care reforms, popularly known as Obamacare, need to be "repealed and replaced with something much less expensive," after the government announced that premiums for some insurance buyers would increase by 25 percent next year.

Clinton has called for changes in the health-care plan, not its repeal. It is used by the minority of Americans who do not have health insurance provided by their employers, but with rising costs, insurance carriers have been dropping out of the program, leaving consumers with fewer choices.

The Clinton campaign says that 20 million people who have insurance because of the law's passage in 2010 would be left without health-care coverage if the law is revoked.

Campaign 2016 Clinton
Democratic presidential candidate Hillary Clinton speaks at a campaign event at University of North Carolina at Charlotte, Oct. 23, 2016.

Clinton encouraging early voting

Clinton is continuing to promote early voting, with Democrats hoping to amass a lead in the many states that allow early voting to make it more difficult for Republicans to catch up on the actual Election Day.  By one estimate, at least seven million voters have already cast ballots.

"We've got to get people turning out," she told one interviewer. "That's the most important thing we can do."

WATCH: Clinton on importance of this election

Obama, a staunch Clinton advocate, said Monday at a fund-raising event in California: "We want to win big. We don't just want to eke it out, particularly when the other guy's already started to gripe about how the game is rigged."

Clinton, confident of winning, routinely calls Trump unqualified to be the American leader, saying he needs to be repudiated at the ballot box. She has made a point in recent days of supporting Democratic candidates for Congress, where Republicans now have a majority in both the Senate and House of Representatives.

No fundraising for party

Also Tuesday, Trump campaign finance chairman Steven Mnuchin made the unusual announcement that Trump himself will no longer take part in big-money fundraisers, something seen as essential for the Republican Party to support its senatorial and congressional candidates, and thus its overall election hopes.

Trump Victory, a joint fundraising committee by the party and the presidential candidate’s campaign, has wound down after holding its last event last week, Mnuchin told The Washington Post. The candidate will spend the last two weeks of the campaign holding rallies and taking his message directly to the voters in person, he added.

Trump supporters will still hold fundraising events with high-ticket prices, and online donations are still welcome. But most of the funds generated outside the Trump Victory committee go to the candidate rather than to the party’s network of field organizers around the country.

Before October, The Post said, Trump fundraisers had funneled $40 million to the Republican Party’s effort to retain its majority control of both houses of Congress. It is unusual for a presidential candidate to stop appearing at fundraisers so close to Election Day and with the election still relatively close.