(CNN) -- President Donald Trump called on Wednesday for "a major investigation" into voter fraud, following through with baseless claims he has made since November's election, alleging millions of illegal votes during the general election, without citing any evidence.
"I will be asking for a major investigation into VOTER FRAUD, including those registered to vote in two states, those who are illegal and ... even, those registered to vote who are dead (and many for a long time). Depending on results, we will strengthen up voting procedures!" Trump wrote in two consecutive tweets.
Trump's comments on voter fraud came Monday during a meeting with congressional leaders, where he reiterated an unsubstantiated claim that 3-5 million illegal votes cost him the popular vote, according to two sources familiar with the meeting.
On Tuesday, Trump's press secretary Sean Spicer vigorously defended Trump's statement about illegal voters, though neither Trump nor his surrogates could provide evidence that any substantial illegal voting had occurred or influence the popular vote.
Trump faced widespread criticism for his remarks, including from some congressional leaders in his own party, and Democrats have alleged that Republican efforts in the name of fighting voter fraud as a way to halt legal voters who traditionally back Democratic candidates from voting.
"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 at Wednesday's press briefing.
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, mentioning voter fraud in regards to his popular vote loss a number of times since November.
When pushed about whether Trump will call for an investigation into the matter, Spicer said, "maybe we will," adding later that Trump believes in voter fraud based on "studies and information he has."
Spicer did not say specifically which studies the President was using to support his claim of 3 to 5 million illegally cast votes, but a 2014 study by Jesse Richman and David Earnest found more than 14% of non-citizens in 2008 and 2010 "indicated that they were registered to vote." Only US citizens can vote in federal elections.
However, Brian Schaffner, a political scientist at the University of Massachusetts, told CNN on Tuesday that his study that is apparently being cited by the White House was misinterpreted and did not support the administration's claims.
A number of studies have also 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%.
Trump himself -- through his lawyers -- have also argued that there was no evidence of voter fraud in the 2016 election. In a court filing objecting to Green Party candidate Jill Stein's Michigan recount petition, lawyers for the president wrote, "All available evidence suggests that the 2016 general election was not tainted by fraud or mistake."
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