WASHINGTON — Barack Obama changed the electoral map when he won the presidency in 2008.

He took the mega-swing state of Florida - which once had tipped the presidency to George W. Bush - seized North Carolina and Virginia away from the Republicans to plant a foothold in the upper South, battled within an inch of taking a perennial Midwest battleground in Missouri and moved blue-tinged Washington state solidly into the Democratic column.

Now, with his formal declaration of candidacy for re-election Monday, Obama invites the question: Can he do it again? Can he hold the states he won in 2008? Win those that barely eluded his grasp? Or will he find himself on the defensive, the landscape changing under his feet, fighting to hold on?

Overall, the president's prospects look mixed. He has middling approval ratings, unemployment remains high, and voters gave his Democrats a drubbing in the 2010 elections. At the same time, unemployment is dropping, but U.S. troops remain in harm's way in Afghanistan, Iraq and off the coast of Libya. A budget fight with Congress looms that could stretch through 2012.

Obama will wage a massive campaign, using the power of the presidency to reach voters early and often. This week alone he'll travel - at taxpayer expense, as all presidents have - to the battleground states of Indiana and Pennsylvania. The official reason is to promote his policies. The other reason? To promote himself.

He'll also raise and spend more campaign money in this election cycle than anyone in history; he's widely expected to top $1 billion. He'll use it to target voters who supported him in 2008, such as blacks, Hispanics and the young, who sat out the 2010 elections, when he wasn't on the ballot.

He'll use the cash to reach states he needs to win, while all but ignoring those he can take for granted, such as Illinois. His aides talk about trying to win solidly Republican states such as Arizona, Georgia and Texas, but Republicans counter that he better worry about holding on to Florida, North Carolina and Virginia.

"Today, the conventional wisdom is that Obama can't carry some of the states he carried in 2008, because those were ideal circumstances," said Larry Sabato, a political scientist at the University of Virginia. "But we don't know that."

At the same time, he added, "If it's a close race, Obama may be hard-pressed to carry Indiana and North Carolina again."

For an early look at the political landscape, here are snapshots of four potential battleground states. The president's campaign didn't respond to requests for comment.

North Carolina: One of Obama's biggest wins in 2008 was North Carolina, the first time the state went Democratic since it voted for Jimmy Carter in 1976.

Obama was buoyed then by the state's black electorate and a wave of Northern transplants who've changed the political demographics in the Tar Heel State. More than a fifth of the electorate counts itself as unaffiliated to any party.

But at this point in the 2008 campaign, North Carolina's unemployment rate was 5 percent. After Obama's election, the jobless rate shot up to a high of 12.1 percent in January 2010, and is now 9.7 percent. Last year Democrats lost a U.S. House seat in North Carolina, and they lost control of both houses of the state legislature.

Obama's determination to retain North Carolina is evident in the Democrats' choice of Charlotte to host the party's 2012 convention.

Robin Hayes, the chairman of the North Carolina Republican Party, said that one of the biggest differences in 2012 is that his party would be better prepared for the Obama political organization.

"The president and his group did a much better job of organizing through the Internet, through social networking, through every possible means to identify and get their folks to the polls. They outworked and outmaneuvered us in the last election," said Hayes, a former congressman who was unseated in the Democratic wave of 2008. "That is not going to happen this time."

Florida: Obama won Florida in 2008 by three percentage points, the first Democrat since Jimmy Carter to top 50 percent there. Since then, the Democrats have lost four seats in the U.S. House of Representatives, failed to win back the governor's office and lost seats in both houses of the state legislature.

The state's jobless rate remains higher, at 11.5 percent, than the 8.8 percent national average, but it's improving slowly. Democrats point to the recovering economy and rosier retirement accounts for the state's many retirees as early signs that people there could feel better about the incumbent by next year.

Missouri: Obama came within 4,000 votes of winning Missouri in 2008, one major Electoral College prize that's always up for grabs. He could face higher odds this time around, unless the political landscape shifts significantly.

His popularity in the state has plunged in the last two years, largely because of his health care overhaul. Missouri voters overwhelmingly endorsed a ballot measure last year to reject the law's insurance mandate.

At the same time, Democrats lost a U.S. House seat in 2010, while Republicans added to their majorities in the state legislature.

John Hancock, a top Republican strategist in the state, said he thought it was unlikely that the president would win the state, regardless of who his opponent was.

"Things would have to change dramatically," Hancock said. "If Obama wins Missouri, it's not going to be close. He will be re-elected by a lot."

Washington State: In the West, the president will try to cement his party's newfound hold on Washington as the new anchor of a solidly Democratic West Coast.

Democrats and Republicans had fought hard over the state for decades. When Obama won the state with 57.7 percent in 2008, it was the biggest margin of any candidate since Lyndon Johnson's landslide in 1964.

There have been signs of erosion. Sen. Patty Murray, D-Wash., won a fourth term last year, but saw her tally drop to 52 percent, her lowest ever. Democrats also lost a U.S. House seat in 2010 and lost seats in the state legislature, but held their dominant majorities.