The second day of a hearing on whether Pennsylvania's new voter identification law should take effect for the Nov. 6 election has started with a University of Washington professor defending how he came up with an estimate that more than 1 million registered voters lack a photo ID that's valid under the law.
The professor, Matt Barreto, began testifying Thursday in a case seeking to block the law this year while state judges consider a challenge to its constitutionality.
The law is among the nation's toughest, and is the subject of a furious debate over voting rights ahead of this year's presidential contest.
The hearing could last a week.
Meanwhile, the U.S. Department of Justice is looking at whether Pennsylvania's law complies with federal laws.
Republican Gov. Tom Corbett signed the law in March after it passed the Republican-controlled Legislature. Every Democrat voted “no.”
Check here for the Pennsylvania voters' photo ID requirements.