Jonathan Zimmerman teaches history at New York University and lives in Narberth. He is the author of "Small Wonder: The Little Red Schoolhouse in History and Memory" (Yale University Press).

That's because I voted several weeks ago. So have millions of other Americans, via absentee ballot and early voting. They're turning a formerly public act into a private one, which should worry all of us, no matter where we vote.

Across the United States, absentee ballots now account for almost 20 percent of votes. Two states, Oregon and Washington, conduct their elections entirely by mail. And in seven others, more than half the votes in the last presidential election were cast before Election Day.

Why is that a problem? One reason is the potential for fraud. Despite the recent spate of voter-ID laws in Pennsylvania and other states, a recent Carnegie-Knight study found just 10 purported cases of voter impersonation at the polls nationwide since 2000; by contrast, there were nearly 500 allegations of absentee-ballot fraud. Here in Philadelphia, a federal judge overturned the results of a 1993 state Senate election because of forged absentee ballots....