Pennsylvania takes the nickname the Keystone State, and the 21 electoral votes it offers could help decide the election between Sen. Barack Obama and Sen. John McCain.

Only three states -- California, Texas and Florida -- hold a bigger stake in the Electoral College. While the state has gone blue the last four elections, 2004 came down to a slim 2 percent win for Democratic Sen. John Kerry, according to 270ToWin.com.

The site also has the state leaning to Obama after late-August polls showed him with 49 and 46 percent of the vote. Those Quinnipiac and Zogby surveys, though, also showed 9 and 17 percent of voters still waiting to make up their minds.

Those tight margins make the state an attractive target for McCain.

The Democratic worry is that Obama may have trouble drawing the white, working-class votes that are important in the state. That group's support for Sen. Hillary Clinton helped her to a 10-point win in the Democratic primary, but she had the support of popular Gov. Ed Rendell.

In late August, Rendell said on WashingtonPost.com admitted there could be problems.

"Before I can tell you Pennsylvania is in the bag we have to do a better job with our message," he said.

The lynchpin, however, tends to be the area around Philadelphia.

Former Vice President Al Gore, for example, took the state by just over 204,000 votes; he won Philadelphia County by 348,000 votes, according to TheRoot.com. Kerry won the state by 144,000 votes and Philadelphia by 412,000.

RightPundits.com quoted a Michael Smerconish column from February that suggested that McCain's moderate social views and general support for the war in Iraq could make him attractive.

TheRoot said, however, that the selection of Scranton native Joe Biden as Obama's running mate could help him gain precious votes to hold on.