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 study’s 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 author’s “best” estimate was that 25.1% of non-citizens were illegally registered to vote.