by DANIELLA SILVA – President Donald Trump continued to perpetuate unsubstantiated and debunked claims of election irregularities Wednesday morning by promising a "major investigation" into what he described as "voter fraud."
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The announcement comes after questions over Trump's repetition of a widely disproved claim that millions of "illegal" votes cost him the popular vote in the presidential election.
Trump tweeted Wednesday morning that he would ask for an investigation into voter fraud, including alleged votes by undocumented immigrants, people who are allegedly registered to vote in more than one state and "those registered to vote who are dead (and many for a long time)."
The president said that depending on the results of the investigation, he would call for "strengthening up voting procedures!"
I will be asking for a major investigation into VOTER FRAUD, including those registered to vote in two states, those who are illegal and....
— Donald J. Trump (@realDonaldTrump) January 25, 2017
even, those registered to vote who are dead (and many for a long time). Depending on results, we will strengthen up voting procedures!
— Donald J. Trump (@realDonaldTrump) January 25, 2017
Trump's tweets come after the White House doubled down on Tuesday that the president believed the debunked claim that millions of people voted illegally, costing him the popular vote.
Democratic nominee Hillary Clinton beat Trump by nearly 3 million in the popular vote but did not secure the number of electoral college votes necessary for a victory.
"The President does believe that," White House Press Secretary Sean Spicer told reporters on Tuesday, just one day after pledging to tell the public "the facts as I know them."
"He's stated that before, I think he has stated his concerns about voter fraud and people voting illegally during the campaign and continues to maintain that belief based on studies and evidence people have presented to him," he said.
Related: Democrats' Popular Vote Advantage Is Growing But That May Not Equal Election Wins
Two sources told NBC News that Trump spent the first ten minutes of a bipartisan meeting with congressional leaders at the White House on Monday talking about the campaign and repeating the allegation that 3 to 5 million people voted illegally.
Those figures appear to come from two different studies, but authors of both have come forward to say that their studies do not support theories of massive voter fraud.
A 2012 Pew report found millions of invalid voter registrations due to people moving or dying, but the report's author, executive director of the Center for Election Innovation & Research David Becker, said in late November that the study found no evidence of voter fraud.
A second study was a highly criticized work by Old Dominion University professors who found 14 percent of non-citizens said saying they were registered to vote. The study was based on a sample of a few hundred respondents.
One of the authors said before the presidential election that Trump's campaign was exaggerating the study's findings.
"Both sides of the debate on non-citizen voting have exaggerated our findings concerning non-citizen representation," political scientist Jesse Richman wrote.
"There are many on the left side of that debate who have relentlessly sought to discredit our results and want to push the level of estimated non-citizen participation to zero. On the right, there has been a tendency to misread our results as proof of massive voter fraud, which we don't think they are. Our focus has been on the data, rather than the politics."
The debunked claim was furthered by conspiracy theorist Alex Jones on his website Infowars.
Trump's comments have been criticized by officials on both sides of the aisle, with GOP Senator Lindsey Graham pleading with Trump to stop repeating the claim.
"To continue to suggest that the 2016 election was conducted in a fashion that millions of people voted illegally undermines faith in our democracy," Graham said.
The National Association of Secretaries of State, which includes many Republicans, also took issue with Trump's claim.
"We are not aware of any evidence that supports the voter fraud claims made by President Trump, but we are open to learning more about the Administration's concerns," the group said in a statement released yesterday. "In the lead-up to the November 2016 election, secretaries of state expressed their confidence in the systemic integrity of our election process as a bipartisan group, and they stand behind that statement today."