The truth behind Trump’s biggest illegal voter claim

The roots of the statistic are found in an article, “Do non-citizens vote in U.S. elections?”, external, published in the journal Electoral Studies in 2014.

Written by three academics led by Jesse Richman, an associate professor at Old Dominion University in Virginia, the paper says the “number of non-citizen voters… could range from just over 38,000 at the very minimum to nearly 2.8 million at the maximum.”

Mr Richman and his colleagues did not comb through voter rolls or personally survey immigrants to come to that conclusion, but instead relied on a data set from a long-running Harvard-backed survey called the Cooperative Election Study, external (CES).

The CES included a number of people who self-identified as non-citizens and indicated that they had voted in the 2008 and 2010 elections.

But the people behind CES have repeatedly rejected the conclusions of Mr Richman’s paper, which attracted controversy and attention before and after the 2016 presidential election.

Brian Schaffner, a Tufts University professor who is one of the CES co-principal investigators, told the BBC that it’s not possible to draw statistical conclusions from a relatively small number of survey participants.

The CES is intended to be a survey of legal voters, and only 339 out of the nearly 34,000 in the 2008 survey said they were non-citizens. That does not constitute a representative sample of the population, Schaffner said.

Various respondent errors and further variables may have also affected the accuracy of that data pool, he added.

In recent years, the CES has included more detailed questions about citizenship and registration to increase its accuracy.

Mr Richman, the author of the Electoral Studies article, drew on that data to conclude in 2023 that 1% of non-citizens were registered to vote. He further estimated half of that number voted in the 2022 midterm elections.

But the CES survey officials maintain that their study is not suitable to create an estimate of non-citizen voting.