To reverse a 24-year trend of presidential Democrats winning Pennsylvania, Romney needs to match or outperform Bush in the four Philadelphia suburban counties, all of which Bush lost except for Chester County in 2004.

Romney also needs high turnout on the western side of the state, where conservative, blue-collar, white voters make up much of the voting demographic. That was largely how Republican Pat Toomey narrowly beat Democrat Joe Sestak for the U.S. Senate seat in 2010.

Perhaps to Romney’s benefit, one of the few hot races in Pennsylvania has been out west. The state’s only real competitive U.S. House race is the 12th District outside Pittsburgh. Western Pennsylvania also gets some bleed-over from the overwhelming attention both the Romney and Obama campaigns have paid Ohio.

Lara Brown, a political science professor at Villanova University, said there is a chance Romney squeaks out a 1- or 2-point win in Pennsylvania, provided certain geographic scenarios go his way. That narrow opening appears to be why the Romney team suddenly is investing time and money in Pennsylvania in the campaign’s final days…

In 2008, Obama received close to 600,000 votes in Philadelphia. In 2010, Sestak, the Democrat who lost to Toomey, received just over 350,000 from the city.