With the first court challenge [NYT] of Pennsylvania's new voter ID law starting this week, state officials admitted that voter fraud, which the law is meant to combat, hasn't been documented:

In a Pennsylvania court filing, the state says it has never investigated claims of in-person voter fraud and so won't argue that such fraud has occurred in the past. As a result, the state says, it has no evidence that the crime has ever been committed. The state also says it won't present "any evidence or argument" that in-person voter fraud is likely to occur on Election Day if the voter ID law isn't enacted.

Abby Rapoport summarizes how many people might be affected by the law, which is one of the strictest in the country:

[W]hen the secretary of the commonwealth did a study in early July, it showed that as many as 758,000 people—or 9 percent of voters—didn't have an ID from the Department of Transportation. Other studies estimate that there could be a million Pennsylvania voters without ID. That's more than the margin of victory Barack Obama had in 2008.

Another analysis suggests that the number might be twice that many. Back in June, the Pennsylvania House Majority Leader Mike Turzai (R) claimed, "Voter ID, which is gonna allow Governor Romney to win the state of Pennsylvania," among his accomplishments. But Emily Bazelon thinks the law may actually hurt Romney: