Rick Santorum has been running strong in the state. The latest poll in Townhall's poll tracker shows the Pennsylvania Republican leading Mitt Romney by fourteen percentage points. A previous poll showed Santorum up by thirteen points. It's likely that Santorum will cruise to victory.
Romney's southern state struggles will continue tonight in Louisiana. The only southern primary that the frontrunner has won has been Florida - and Florida isn't exactly a classic southern state in terms of demographics - though neither is Louisiana. There are fewer evangelicals in Louisiana than in neighboring Mississippi and Alabama and a sizable Catholic population. These two facts would hurt a traditional evangelical candidate, but Santorum's conservative Catholicism will actually be aided. Additionally, despite Louisiana's status as a red state, only 27 percent of voters are registered Republicans, compared to nearly fifty percent of Democrats.
Santorum needs all the delegates he can get at this point to keep the momentum alive and keep up his hopes of having a chance to influence the GOP race. It's possible to sketch a path for Romney to 1,144 delegates - the number anyone needs to secure the nomination - but it's harder and harder to see a viable future for Santorum. Louisiana will give him a modicum of momentum, but after the April 3 mid-Atlantic primaries, there will be a three-week lull. Santorum needs to be able to make the case that his participation is necessary going forward.
Polls will close at 8pm tonight, and look for a winner soon afterwards. FiveThirtyEight has more.