How big is this problem nationally? One district-court administrator estimated in 2005 that up to 3% of the 30,000 people called for jury duty from voter-registration rolls over a two-year period were not U.S. citizens. A September report from the Public Interest Legal Foundation found more than 1,000 noncitizens who had been removed from the voter rolls in eight Virginia counties. Many of them had cast ballots in previous elections, but none was referred for possible prosecution.

The lack of prosecutions is no surprise. In 2011, the Electoral Board in Fairfax County, Va., sent the Justice Department, under then-Attorney General Eric Holder, information about 278 noncitizens registered to vote in Fairfax County, about half of whom had cast ballots in previous elections. There is no record that the Justice Department did anything.

A 2014 study by three professors at Old Dominion University and George Mason University used extensive survey data to estimate that 6.4% of the nation’s noncitizens voted in 2008 and that 2.2% voted in 2010. This study has been criticized by many academics who claim that voter fraud is vanishingly rare. Yet the Heritage Foundation maintains a list of more than 700 recent convictions for voter fraud.