In a report released Thursday examining state voting requirements, the GAO could not document cases of voter fraud.
The study was requested by Sens. Bernie Sanders, I-Vt., Patrick Leahy, D-Vt., Richard Durbin, D-Ill., and Bill Nelson, D-Fla., who asked GAO for details on "any prosecutions or convictions for voter impersonation fraud within each state during the previous 10 years."
The authors told the senators that the report would not address that point because of a lack of data. However, "an earlier report by the Brennan Center for Justice found that substantiated cases of voter fraud were extremely rare," a news release about the study from Sanders pointed out.
That lack of data could punch holes in a frequent argument from lawmakers in states that have passed such requirements, who claim the laws are necessary to combat voter fraud.
The report also documented a substantial increase in voting requirements over the last 10 years. Twenty-one states passed new voter I.D. laws; seven heightened requirements, bringing the total number of states requiring identification to 31.
The battles over voter identification have made headlines this campaign. Earlier this week, a Pennsylvania judge delayed the Keystone State's new photo identification requirement from taking effect until after November's election, asserting that the state had not ensured people could acquire photo identification before then.
Statutes in other battleground states have also come under attack. Two court challenges are under consideration in Ohio and Floridians are fighting back against Republican Gov. Rick Scott's efforts to purge immigrants from the voting rolls.
This story, originally published Oct. 4, has been updated.
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