Both presidential contenders planned to focus on eight battleground states in the final days of the 2012 campaign. But those itineraries have grown since Republicans began pumping millions into traditionally Democratic Pennsylvania, Minnesota and Michigan in hopes of flipping them for Mitt Romney.

Romney and President Obama both returned to the campaign trail Thursday after taking time off to deal with the fallout from Superstorm Sandy, which devastated the East Coast. But even their abbreviated campaign schedules hint at similar strategies for getting to the 270 electoral votes needed to win the White House.

Obama made stops in Wisconsin, Colorado and Nevada on Thursday. Romney made three stops in Virginia.

All four of those states are too close to call and critical to both candidates' victory plans, though none is more important than Ohio, the state political experts believe could decide the election.

Ohio, with 18 electoral votes, favored Obama by about 5 percentage points in 2008, but four years earlier picked Republican President George W. Bush by just 110,000 votes. Now polls show Ohio to be a dead heat between Obama and Romney, both frequent visitors who will be making additional appearances there this weekend.

Rounding out the critical eight states included on the final campaign itineraries are Iowa, New Hampshire and Florida, where polls are deadlocked.

But added to the mix now are Michigan, Minnesota and Pennsylvania, where both sides have started to spend more money. The trio of Democratic-leaning states were once thought to be solidly behind Obama. But his edge in all three has narrowed in recent days.

While Obama aides scoffed at suggestions that Romney could win Michigan -- where his father was once governor -- the tightening polls prompted Obama to start spending money there on new advertising.

"It certainly is a possibility that Romney will win," Jeff Timmer, a Lansing-based GOP strategist, told The Washington Examiner. "I think Romney would still have to overcome the inherent Democratic tendencies of Michigan in a presidential year."

Michigan last backed a GOP presidential candidate in 1988.

In traditionally Democratic Minnesota, polls show Romney closing in on Obama, though Larry Jacobs of the University of Minnesota said it's still unlikely that the state will go Republican because the GOP simply doesn't have the kind of organization needed there to get its voters to the polls.

"It's certainly within striking distance for Romney," Jacobs said. "The problem is, he has no feet on the ground here."

Wisconsin is another state once considered safe for Obama but now looking more like a tossup. Not only is Romney's vice presidential running mate, Rep. Paul Ryan, a Wisconsin native, but Republicans in the Badger State have pumped up their organization and enthusiasm in fighting the recall of Gov. Scott Walker this summer.

As a result, Obama is suddenly spending a lot of time in Wisconsin. He campaigned there Thursday and will return on Saturday and again on Monday.

"You have an incredibly fired-up Republican base here," Wisconsin GOP strategist Mark Graul told The Examiner.