It could turn out to have a bigger effect on Rs than Ds.
My reasoning is based on the power it will give the Judges of Election at any given precinct, where the JoEs will hear the voter's name called when they arrive, with either a D or R after their name. Then when they hear that there is a discrepancy with their ID, the JoE can then apparently decide whether to let the person vote or not, after hearing, or in most cases just knowing by sight, what party the voter belongs to.
At the risk of being labeled a racial profiler, even though this has nothing to do with that, I'm thinking of the two biggest cities in PA. With one million or so more Ds in the state than Rs, particularly in Philly and Pittsburgh, there may be more of a chance of abuse of this power. With the preponderance of Ds in Philly especially, where union passions among others seem most partisan and frankly, contested votes might be more subject to question and the Rs might be more likely to feel the brunt than in the suburbs.
But then one most look at the bigger picture. With Obama's lead growing in PA, and accepting that this whole issue may not affect that outcome, one then must look down ballot where it will only serve to accentuate the one-sided nature of the current incumbents. Where there are more Rs likely to be serving as JoEs, their candidates will be given an increased ability to win. From that perspective, it will make it all the more difficult for the Ds to win in Pennsyltucky/Alabama between and around Philly and Pittsburgh.
Just a thought. Regardless, it's a dumb freaking law as it is written in the short window of time it has to be put into practice, no matter who might be more