It is the kind of thought that rarely passes the lips of a member of the federal judiciary: I was wrong.

But there was Richard A. Posner, one of the most distinguished judges in the land and a member of the United States Court of Appeals for the Seventh Circuit, saying he was mistaken in one of the most contentious issues in American politics and jurisprudence: laws that require people to show identification before they can vote.

Proponents of voter identification laws, who tend to be Republican, say the measures are necessary to prevent fraud at the polls. Opponents, who tend to be Democrats, assert that the amount of fraud at polling places is tiny, and that the burdens of the laws are enough to suppress voting, especially among poor and minority Americans.

One of the landmark cases in which such requirements were affirmed, Crawford v. Marion County Election Board, was decided at the Seventh Circuit in an opinion written by Judge Posner in 2007 and upheld by the Supreme Court in 2008.