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At the top of President Donald Trump's agenda for his discussion with congressional leaders Monday night: relitigating the campaign, including saying "illegals" voting deprived him of a victory in the popular vote.

The claim of widespread voter fraud in the 2016 presidential election, which Trump argued in late November, has been widely debunked.

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Related: With No Evidence, Trump Claims ‘Millions’ Voted Illegally

Two sources confirmed to NBC News that Trump spent about the first 10 minutes of his bipartisan meeting with congressional leaders at the White House talking about the campaign and about how 3 million to 5 million "illegals" voted in the election, causing him to lose the popular vote.

President Donald Trump hosts a reception for House and Senate leaders Monday in the White House. Susan Walsh / AP

NBC News has reached out to the Trump administration for comment about the claims.

The meeting with congressional leaders was described as more a social occasion than a formal session. Senate Majority Leader Mitch McConnell, R-Kentucky, returned to the Capitol on Monday night and said it was "light-hearted," joking that he was most entertained by seeing Trump and Minority Leader Chuck Schumer, D-New York, discuss which New York politicians were common friends.

After the reception, Trump met privately with House Speaker Paul Ryan, R-Wisconsin. Ryan's office described the meeting as substantive and wide-ranging, including discussions of the repeal of the Affordable Care Act and other agenda items for the new administration.

"The speaker and President Trump are eager to continue moving forward on their shared agenda to jumpstart the economy and get the country back on track," a Ryan spokesman said in a statement.