Enough non-citizens illegally vote in U.S. elections to potentially decide close races, a new study suggests.

Old Dominion University political scientists Jesse Richman and David Earnest found, in an article due to be published by the journal Electoral Studies, that 6.4 percent of non-citizens voted in the 2008 elections and 2.2 percent voted in the 2010 midterms.

Although a small share of the total U.S. non-citizen population, those voters may have been enough to swing close races, Richman and Earnest wrote Friday on the Washington Post's Monkey Cage blog.

One example could be the the 2008 Minnesota Senate race that saw Al Franken elected the 60th Democrat in the upper chamber. Franken was elected by a margin of 312 votes, and the authors pointed out that margin is less than a percent of the potential illegally voting non-citizens.

"Our research cannot answer whether the United States should move to legalize some electoral participation by non-citizens as many other countries do, and as some U.S. states did for more than 100 years, or find policies that more effectively restrict it," the professors wrote. "But this research should move that debate a step closer to a common set of facts."

The study used data from the Cooperative Congressional Election Study, a large survey administered by YouGov/Polimetrix to over 50,000 people in the U.S.

The incidence of illegal voting is a hotly contested topic in U.S. politics, with many conservatives supporting voter identification laws to root out ballot fraud. Many on the left have suggested that those measures are intended to reduce turnout among minorities who tend to vote Democratic.

Richman and Earnest found evidence that voter identification laws are unlikely to be effective in reducing illicit voting, regardless of how often it takes place.

"Nearly three quarters of the non-citizens who indicated they were asked to provide photo identification at the polls claimed to have subsequently voted," they explained.