(Reuters) - "Swing" or "battleground" states, which can switch back and forth between the two major parties in U.S. presidential votes and are heavily courted by candidates, will be crucial to deciding the winner of next year's election for the White House.
President Barack Obama visited two such states, Nevada and Colorado, as part of a trip to the West this week.
Here are details of expected battleground states in 2012.
* FLORIDA -
With more than 18 million people, Florida is the fourth most populous state in America, making it the largest swing state with 29 electoral votes.
With Florida's unemployment rate at 10.6 percent, among the worst in the country, Obama faces a tough fight to win again in the state where he defeated Republican Senator John McCain in 2008.
An October NBC News/Marist Poll showed Obama at 45 percent, with former Massachusetts Governor Mitt Romney trailing him by 2 points among potential Republican rivals.
The Republican Party is holding its national convention in Tampa next August to try to win voters in Florida, home to large numbers of Hispanic and elderly voters.
Florida has a large number of Social Security recipients, with a third of its registered voters 60 or older. The federal retirement program has become a hot topic in recent Republican debates. Some Republican candidates like Texas Governor Rick Perry have come under fire in the state for saying the Social Security program is not financially sustainable in its current form.
The state was the center of the hotly disputed 2000 presidential race, with only several hundred votes separating Republican George W. Bush and Democrat Al Gore in Florida. A recount battle delayed the outcome for over a month before the U.S. Supreme Court halted the recount, giving Bush the presidency.
* COLORADO -
Colorado was predominantly a Republican state until Democrats took over the governor's office and both chambers of the Legislature in 2004. In 2008, a large majority of Hispanic and young voters carried Obama to victory there.
Colorado has a jobless rate of 8.3 percent. According to a Project New West poll, which coincided with Obama's visit to the state this week, the president leads Republican contenders.
* NEVADA -
Nevada, where an influx of new residents and a growing Hispanic population led Obama to a 2008 victory, has the highest state unemployment rate in America at 13.4 percent.
The state's stagnant economy makes it a crucial battleground in the 2012 election cycle. Immigration and jobs will be central issues in the Nevada race that will be a fight for six electoral votes. A recent Public Policy Polling survey showed Obama and Romney neck and neck in the state.
* NEW HAMPSHIRE -
Although it has a small population and holds only four electoral votes, New Hampshire is significant as it is an early voting state in the presidential nominating contests. In 2012, its Republican presidential primary will be an important step on the road to deciding the party's nominee.
Obama's approval ratings in New Hampshire have slumped this year. A recent WMUR Granite State poll revealed that 53 percent of adults in the state disapproved of Obama's performance in the White House.
* OHIO -
In Ohio, Obama scored a 5-point victory in 2008. But with 9.1 percent of the state's workers out of jobs and his approval ratings slipping, Obama faces a challenge maintaining support.
At recent campaign-style events at auto plants in the state, Obama claimed credit for the 2009 bailout of the auto industry. His campaign hopes that the move in support of U.S. manufacturing will warm Obama to blue-collar voters.
Obama won Ohio by a 4-point margin over McCain in 2008. But the state went narrowly to Bush in 2004, and is expected to be highly competitive in 2012. Ohio has 18 electoral votes.
* NORTH CAROLINA -
North Carolina has 15 electoral votes. It was a Republican presidential stronghold in recent elections until Obama carried the state in 2008, but polls show his popularity dimming.
A recent Elon University poll put Obama's approval rating at 42 percent in North Carolina, where Democrats will convene their presidential convention in Charlotte next summer.
His campaign has planned to mobilize efforts to compete in North Carolina and Virginia, where a big voter turnout among blacks gave him a boost in 2008.
* VIRGINIA -
Virginia's recent presidential elections were dominated by Republicans until Obama's victory in 2008. In 2012, Obama faces a battle holding the state, where polls show him losing supporters. The state has 13 electoral votes.
A Quinnipiac University poll this month showed Obama's approval ratings at 45 percent in Virginia and put Republican presidential contenders Mitt Romney and Herman Cain in a statistical dead heat with him in a theoretical matchup.
* PENNSYLVANIA -
Pennsylvania has favored Democratic presidential candidates since 1992. In 2008, Obama won the state's 21 electoral votes with 55 percent of the vote.
Pennsylvania will account for 20 electoral votes this year and is considered critical to Obama's 2012 aspirations.
With a jobless rate of 8.3 percent, the state's economic woes have been dragging Obama down in recent polls.
According to a Quinnipiac University poll last month, 51 percent of voters surveyed said Obama did not deserve a second term.
* WISCONSIN -
Democrats have won Wisconsin in the past six presidential elections. But after Obama's sweeping win in the state in 2008, growing concern over his economic policies helped lead to a Republican wave in the state's 2010 elections.
The state, which has 10 electoral votes, drew attention this year for its dispute between Republican Governor Scott Walker and Democratic-leaning labor unions over collective bargaining rights. The 2012 election is expected to be close as the state is grappling with slow job growth and a sluggish economy.