A new paper by Jesse Richman, Gulsham Chattha, and David Earnest, available on first release in Electoral Studies, makes the controversial claim that:
We find that there is reason to believe non-citizen voting changed one state’s Electoral College votes in 2008, delivering North Carolina to Obama, and that non-citizen votes have also led to Democratic victories in congressional races including a critical 2008 Senate race that delivered for Democrats a 60-vote filibuster-proof majority in the Senate…
The authors follow a creative strategy by leveraging the large sample sizes in the Cooperative Congressional Election Study in 2008 and 2010, and vote validation that occurred in 2008, to show that somewhere between 3.3%-25.1% of non-citizens were registered, and 1.5%-11.3% of non-citizens turned out to vote.
Extrapolated to the general population, they estimate anywhere from 38,000 to 2.8 million ballots were cast by non-citizens, and the bulk of these were Democratic votes (see figure above, reproduced from the paper).
The study is the first careful look at non-citizen voting that takes advantage of vote validation, and is almost certainly going to enter into the debate over photo ID.