Governor Tom Corbett and Pennsylvania Republicans are considering legislation to change the allocation of Pennsylvania's Presidential electors. Instead of awarding all 20 on a winner take all basis, the plan by Senate leader Dominic Pileggi would switch to the Congressional district model currently in use by Nebraska and Maine.
In Nebraska and Maine, the statewide popular vote for President only determines two Presidential electors, the two representing the states' Senators. The remaining votes are allocated according to the popular vote in each House district. Nebraska's second district breaking for Obama in 2008 did not shape the election, but if Pennsylvania follows this model, then the 2012 Electoral College scenarios change significantly. Here's how.
According to my own 2012 Create your own Electoral College tool, the base 2008 map with the 2012 apportionment starts the President with a 359-179 Electoral College lead. However if we swing five states (Florida, North Carolina, Virginia, Indiana, and Ohio) and one district (Nebraska 2) that George W. Bush won twice, Barack Obama's lead is reduced to 272-266.
Enter Pennsylvania. In 2008, Obama won 9 of 19 House districts, plus the statewide vote. If he were to win 9 of Pennsylvania's 18 districts in 2012 plus the statewide vote, he would earn 11 of the state's 20 votes, with the remaining 9 going to the Republican.
Subtracting 9 from Obama in the above scenario, and adding 9 to the Republican, changes the result. The Republican now wins 275-263. Republicans would have much less need to hope for a turnaround in states like Nevada or Colorado, or to win a coin flip in swing states like New Mexico, New Hampshire, or Iowa. Five states that went for Bush twice would win the election.
It's obvious why Pennsylvania Republicans are considering this. It changes the tactical situation of the race, with an 18 point swing toward the Republicans. The Pennsylvania plan is as meaningful as winning Colorado's 9 electoral votes, and that's without even changing the mood of the electorate.