In 2014, the academic journal Electoral Studies published a groundbreaking study by three scholars who estimated how frequently non-citizens were illegally voting. Based on data for the 2008 presidential and congressional elections, the study found that:
roughly one quarter of non-citizens in the U.S. were likely registered to vote.
6.4% of non-citizens actually voted.
81.8% of them reported voting for Barack Obama.
illegal votes cast by non-citizens likely changed important election outcomes in favor of Democrats, including Electoral College votes and a pivotal U.S. Senate race that enabled Democrats to pass Obamacare.
The studys voter registration rate was estimated with data from two key sources:
A national survey in which 14.8% of non-citizens admitted that they were registered to vote.
A database of registered voters that reveals what portion of the surveyed non-citizens were in fact registered even though they claimed not to be registered.
By combining these data, the authors best estimate was that 25.1% of non-citizens were illegally registered to vote.