The handful of Florida counties that could decide the 2016 election

Florida has once again become an important battleground state and could decide the election this year. In the past two decades, presidential candidates have won Florida by margins of only a few hundred thousand votes. The most extreme case was in 2000, when George W. Bush won by 500 votes. With Florida, he won the presidency.

Polls in this swing state give Democratic nominee Hillary Clinton the lead. But Eduardo Gamarra, a political scientist at Florida International University, warns that it's still too early to tell. "The race has not been decided," he says. Statistically, Trump still has a shot.

The battle for the state's 29 electoral votes is concentrated in a dozen counties in central Florida - the famous I-4 corridor, between Orlando and Tampa - and the Southeast. In 2014, both of these areas were home to 56% of the state's voting-age citizens. Among eligible voters, nearly two million were Hispanic.

THE HEARTLAND: A CHANGING AND COVETED VOTE

The I-4 corridor is critical to the election, says University of South Florida professor Susan MacManus. It’s home to a large number of registered voters, and divided almost evenly between Republicans and Democrats.

Among Central Florida counties, Hillsborough is a good indicator for the state. "Traditionally, it has been the best predictor of how the state will vote in the presidential election," says MacManus.

THE SOUTHEAST: EVERY VOTE COUNTS

In Broward, Palm Beach and Miami-Dade counties, voter turnout will be key. All three have voted overwhelmingly Democratic (especially Palm Beach and Broward), so Republicans will have to go after every vote.

Democratic candidate John Kerry won in these three counties in the 2004 election, in some cases with more than 60% of the vote. But George W. Bush won more than 800,000 votes in those counties - giving him a victory in Florida.

Cubans in South Florida are critical for Republicans, says Gamarra, although he says that this community is changing. On one hand, each new generation tends to lean more Democratic. On the other hand, many older Cuban Americans "feel abandoned" by the Republican Party and disappointed by Trump, but are unwilling to vote for Clinton.

WHO CAN MOBILIZE MORE VOTERS?

Ahead of the election, the key may be the ability of the two parties to register new voters. According to MacManus, Republicans are mobilizing first-time voters. These are people who "are tired of politics as usual and are attracted to Trump," she says.

But the same ideas that are seducing new Republican voters may also encourage votes for the Democrats. "It's a paradox,” Gamarra said. “What Trump says about immigration is what has succeeded in mobilizing whites, but it is also what’s probably mobilizing Hispanics to participate."

The question is whether new Hispanic voter registrations will be enough to offset an increase in Trump voters.

So far, more than 12 million people are registered to vote in Florida. Since January of this year, more than 230,000 new voters have registered as Republicans. Democrats added more than 150,000 voters in the same period.

MORE HISPANIC VOTERS

There are nearly two million Latinos registered to vote in Florida, mostly as Democrats. Since the 2008 election, the number of Hispanics registered as Democrats has grown by 43%. Among Republicans, the number of registered Latino voters grew by 12%.

The Democratic Party is working hard to register Puerto Ricans newly arrived to the I-4 region, where the Puerto Rican population has increased greatly in recent years, MacManus says. In 2010, 264,939 Puerto Ricans resided in Orange, Osceola, Polk and Seminole counties. Four years later, that number was 324,061.

The candidates are also eying independents and Hispanic millennials in the state. Nearly three million voters in Florida don't identify with a party. Of these, more than 630,000 are Hispanic -- more than the number of Latino Republicans. Gamarra explains that this number reflects a national pattern, in which the number of independents "has grown significantly."

Young Hispanics are reluctant to take sides. In the United States, Latinos under age 30 make up 44% of eligible Hispanic voters, says Gamarra. "Characteristically, millennials don’t register or vote. And that's the big concern of strategists, especially the Democrats."

A number of questions remain: How Hispanics will vote, how many new voters Trump will attract, who independents and young people will choose. "This year, all the rules, all the knowledge we have, is in question," Gamarra says.

SOURCE: Juan Clavijo (Cifras & Conceptos), American Community Survey (Census Bureau), Pew Research Center and Florida Division of Elections.