Mitt Romney's campaign has begun buying air time for the final days of the campaign in Pennsylvania, a sign it's trying to expand the presidential map in the last week of the campaign.

Romney has so far purchased airtime in the Philadelphia media market on Nov. 5 and 6 — Election Day and the day before — according to a Republican tracking the buys. The full size of the reservation is unclear.


His campaign has talked for weeks about making a run at Pennsylvania, a large Democratic-leaning state that would be a game-changer for Romney. If he pulls off a surprise win there, the state's 20 electoral votes would give him many more paths to victory in the Electoral College.

Team Romney recently made a small ad buy of just $30,000 in Minnesota that may have been a head fake. As the size of the Pennsylvania buy is not yet clear, it's uncertain whether he's making a serious run at the state or just forcing President Obama to spend resources there as well. 

A number of Republican outside groups including Restore Our Future have begun spending heavily in Pennsylvania and Obama's campaign is also reserving air time there, a sign they're taking the challenge seriously.

Most recent polls shows Obama with a lead of 4 to 6 points in the state.

The Obama campaign released a statement Tuesday calling the Pennsylvania ad buy a sign of last-minute desperation on Romney's part. 

"Now, like Republicans did in 2008, they are throwing money at states where they never built an organization and have been losing for two years," said Obama campaign manager Jim Messina. 

"Let’s be very clear, the Romney campaign and its allies decision to go up with advertising in Michigan, Pennsylvania and Minnesota is a decision made out of weakness, not strength."

Restore Our Future has purchased a $2.2 million ad buy in Michigan, another state where Obama has consistently led in polls. Romney's campaign has so far not bought air time in Michigan. 

Messina said Obama is "leadiing or tied in every battleground state across the country," while Romney "has not been able to put away a single battleground state" in the closing weeks of the campaign. 

“Voters who haven’t heard from the Romney campaign in two years will see this desperation for what it is," Messina said. 

Updated at 1:30 p.m.