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ABC News' Michael Falcone reports:

With exactly one week to go before Election Day, the Romney and Obama campaigns are both planning to air television ads in Pennsylvania - a state that had long looked to be safely in the president's column, but which ABC News and other outlets shifted into "lean Democratic" territory last week.

According to a source tracking television ad buys in the battleground states, the Romney campaign is reserving air time in the Philadelphia media market.

The Romney campaign's move comes close on the heels of the news that the Obama campaign is also going on the air in the Keystone State. The initial size of their ad buy is $650,000 on broadcast and cable in the Philadelphia and Pittsburgh areas from Oct. 31 through Nov. 6.

It is possible that both campaigns' investments will grow. And Romney's buy is bolstering the effort of several GOP outside groups, including the pro-Romney super PAC, Restore Our Future, which on Monday announced a $2.1 million closing-week ad blitz across the state.

The Romney campaign's political director, Rich Beeson, released a new memo on Tuesday arguing that Pennsylvania is well within the Republican candidate's reach.

"With one week to go, and 96 percent of the vote on the table on Election Day in Pennsylvania, this expansion of the electoral map demonstrates that Governor Romney's momentum has jumped containment from the usual target states and has spread to deeper blue states that Chicago never anticipated defending," Beeson wrote in the memo, adding: "While the Obama campaign would like to wish it is 2008, the reality is that they are now forced to 'play defense' in least six states (Pennsylvania, Minnesota, Colorado, New Hampshire, Iowa and Wisconsin) that they once believed were 'safe' Obama wins."

The Romney campaign has long talked about broadening the map of states where it could be competitive, and in his memo, Beeson also pointed to Minnesota as further evidence the strategy was working.

Both campaigns have bought up last-minute airtime there, and ABC News also recently changed the state's rating from "safe" to "lean" Democratic. However, the most recent polling still gives Obama the edge in both there and in Pennsylvania.

Although President Obama remains in Washington to deal with the aftermath of Hurricane Sandy, his campaign dispatched former President Bill Clinton to campaign in Minneapolis and Duluth on Tuesday.

"We're not going to take anything for granted," Obama campaign manager Jim Messina said on a conference call with reporters on Monday. "They understand they're not going to win Ohio, and now they're getting desperate and wanting to put other states into play. And because of the incredible enthusiasm and support of our on line donor base, we're able to have the resources to match them and we're going to do that."

The Obama campaign regularly ran television ads in Pennsylvania during the spring and summer, before curtailing their spending there. That changed this week.

"We're going to take every precaution," Obama strategist David Axelrod said on Monday. "We're not going to surrender any state to them in terms of the airwaves."

A Romney aide characterized the campaign's attempt to turn Pennsylvania and Minnesota (both of which voted for Obama four years ago) into red states as an "effort to get to 300 not just 270 electoral votes."

"We've ensured that we have every dollar we need going toward staff, voter contact, get-out-the-vote, advertising and digital outreach. We've bought all the TV that can be bought," the aide said in an interview with ABC News. "We've done everything that we can do, and now we're expanding the map into areas that the president shouldn't even be thinking twice about."

But an Obama campaign aide disagreed with that framing.

"They are doing this because they don't have a path to 270, currently," this aide said. "They're not going to win Ohio, they're down in Virginia. So they need to expand the map, otherwise they're in trouble."

ABC News' Devin Dwyer contributed reporting.

Full memo from Romney campaign political director Rich Beeson :

MEMO: PENNSYLVANIA

RICH BEESON | 30 OCTOBER, 2012

Rendell: 'Startling upset' for Romney 'a possibility' in Pennsylvania

When Governor Ed Rendell made these comments last week, he was clearly sending a desperate call to Chicago for help in the Keystone State. At the time, his comments were met with derision and scorn from the Obama High Command who were feeling secure in their own predictions of a landslide victory.

What a difference a few days makes. Not only has Minnesota has been moved to "Lean Dem" and the Obama Campaign is up in that state with a significant television buy, but the Chicago gurus have heeded Governor Rendell's plea and are buying television in Pennsylvania and sending the Vice-President in to help prop up their flagging campaign.

With one week to go, and 96% of the vote on the table on Election Day in Pennsylvania, this expansion of the electoral map demonstrates that Governor Romney's momentum has jumped containment from the usual target states and has spread to deeper blue states that Chicago never anticipated defending.

In 2007, then candidate Obama said he would accept the Presidential public financing and its attendant limits on spending. We all know he broke that pledge and went on to raise $745 million while Senator McCain kept his word and ran under the limits of public financing.

Governor Romney's strong fundraising efforts have enabled our campaign to compete with the Obama effort on a level playing field, helping us shape the landscape for this Presidential election.

As a campaign, we will put more resources into the target states in the final week, than previous GOP campaigns have been able to do in the final 10 weeks. The Romney campaign has the resources to expand the map in ways that weren't possible in past cycles (without reducing any effort in any other target state). After fully funding the paid media effort, the ground operations and the voter contact programs, Governor Romney's message of bringing real recovery continues to resonate with voters, volunteers, and donors.

Pennsylvania presents a unique opportunity for the Romney campaign. Over the past few years we have seen Pennsylvania voting for a Republican senator and a Republican governor, and Republicans win control of the State House in addition to the State Senate. The western part of the Keystone State has become more conservative (and President Obama's war on coal is very unpopular there), and Mitt Romney is more competitive in the voter-rich Philadelphia suburbs than any Republican nominee since 1988. This makes Pennsylvania a natural next step as we expand the playing field.

While the Obama campaign would like to wish it is 2008, the reality is that they are now forced to "play defense" in least six states (Pennsylvania, Minnesota, Colorado, New Hampshire, Iowa and Wisconsin) that they once believed were "safe" Obama wins.

As the Romney-Ryan message continues to resonate and GOP momentum continues to build, we are adding Pennsylvania to the long list of states where we are expending significant resources in order to bring real recovery to the country, while continuing to implement and fund full-scale efforts in all the target states.

Rich Beeson is the Political Director for Romney for President, Inc.