TALLAHASSEE, Fla. (AP) — A large, diverse and transient population lured by Florida’s sandy shores, warm winters and lower cost of living has helped turn it into a fiercely contested swing state in modern presidential elections.

From the end of Reconstruction through 1948, the Democratic presidential candidate carried Florida in 17 of 18 elections, a streak that was part of what then was the party’s firm grip on the South.

But since 1952, Democrats have carried Florida in just four of 15 elections, winning the White House each time: Lyndon B. Johnson in 1964, Jimmy Carter in 1976, Bill Clinton in 1996 and Barack Obama in 2008.

It could have been five of 15 elections for Democrats if not for the contested 2000 race. The White House ultimately went to George W. Bush after the Supreme Court declared the Republican the winner in Florida over Democrat Al Gore by a mere 537 votes.

Which way Florida swings in presidential elections is largely due to the transient nature of its population. A constant influx of new residents, like Erin Mitchell, can make a difference from one election cycle to the next.

Mitchell moved to Florida from Boston and had lived in Chicago before that. She used to be a Democrat, then registered as a Republican and is now an independent. She voted for Republican George W. Bush in 2000, but went for Democrats John Kerry in 2004 and Barack Obama in 2008.

And Mitchell lives in St. Petersburg, which is about half way up the peninsula in a part of a key swing region of the state that stretches from Tampa, on the Gulf Coast, to Daytona Beach, on the Atlantic Ocean.

She says she’s frustrated with Obama, but doesn’t trust his Republican challenger, Mitt Romney. It’s to the point where she’s thinking of casting a vote for a third-party candidate, except she feels it would be a wasted vote.

“This is actually a really tough one for me. I will not vote for Mitt Romney,” said Mitchell, 41, who does marketing work with authors. “I just don’t buy it. Whatever he is he’s selling, it just doesn’t work for me. In the end I probably will end up voting for Obama.”

Florida has nearly 4.6 million Democrats and more than 4.1 million Republicans. But the Democrats include a lot of north Florida “Dixiecrats” — Southerners who vote Republican but register as Democrats because generations before them did.

About 2.4 million Florida residents aren’t registered with a party.

Of the 19 million people who helped Florida become the country’s fourth most-populous state, less than one-third were born in the state, according to the census. Nearly one in five Florida residents is foreign born. The state is a microcosm of America, with a mix of large urban areas like Miami, Orlando, Jacksonville and Tampa, and large swaths of rural farmland.

There are transplanted New Englanders and New Yorkers in southeast Florida and Midwesterners in southwest Florida. There’s a huge Hispanic population in Miami-Dade County that’s a near equal mix of Cuban Americans and non-Cuban Latinos from Central and South America, Mexico and Puerto Rico.

Florida also has Jewish, Haitian-American, active and retired military populations and just retirees in general.

The state is a challenging one for candidates to compete in because of its size, and has become a fiercely contested one since the 2000 White House race.

Florida voted Republican that year, for Bush, and for Bush again during his re-election campaign in 2004.

Obama won Florida in 2008. He and Romney are now campaigning hard to be declared the victor in the state on Nov. 6.

In terms of its number of votes in the Electoral College, Florida is the largest of the nine states both sides are competing hardest to win. Florida has 29 of the 270 electoral votes a candidate needs to become the next president.

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