WASHINGTON (CNN) -- President Donald Trump believes millions of votes were cast illegally in last year's election, White House press secretary Sean Spicer said on Tuesday, but he wouldn't provide any concrete evidence for the claim, which has long been debunked.
"The President does believe that, I think he's stated that before, and stated his concern of voter fraud and people voting illegally during the campaign and continues to maintain that belief based on studies and evidence people have brought to him," Spicer said.
Pressed for what evidence exists, Spicer would say only that Trump "has believed that for a while based on studies and information he has."
When pushed about whether Trump will call for an investigation into the voter fraud, Spicer said, "maybe we will."
Trump surprised the top Republicans and Democrats in Congress on Monday when, during a dinner at the White House, he repeated his claim that millions of undocumented immigrants voted for Hillary Clinton -- allegedly depriving him of the popular vote, according to two sources familiar with the meeting.
Trump lost the popular vote to Hillary Clinton by nearly 3 million votes in November, but won the Electoral College and thus the presidency. Trump, however, has seemingly been fixated on the popular vote, tweeting after the election in November that, "In addition to winning the Electoral College in a landslide, I won the popular vote if you deduct the millions of people who voted illegally."
A number of studies have found no evidence of widespread voter fraud.
The Truth About Voter Fraud, a report written by experts at The Brennan Center for Justice, found voter fraud rates were between 0.00004% and 0.0009%.
"Given this tiny incident rate for voter impersonation fraud, it is more likely, the report noted, that an American will be struck by lightning than that he will impersonate another voter at the polls," reads the report.
South Carolina Republican Sen. Lindsey Graham slammed Trump earlier Tuesday over the claim.
"I wasn't there, but if the President of the United States is claiming that 3.5 million people voted illegally, that shakes confidence in our democracy --- he needs to disclose why he believes that," Graham told CNN.
The-CNN-Wire™ & © 2017 Cable News Network, Inc., a Time Warner Company. All rights reserved.