President Trump says that as many as 5.7 million undocumented immigrants might have voted in the 2008 presidential election. That's when Barack Obama defeated John McCain.
This statistic came from a group called Just Facts. They are a New Jersey firm consisting of conservatives and libertarian policy analysts. The group concluded that there was a minimum of nearly 600,000 illegal immigrants who voted in that election and a maximum of 5.7 million.