CHICAGO (CBS) — President Trump is once again drawing some criticism; this time for claiming millions voted illegally in the November election.

White House Press Secretary Sean Spicer didn’t provide any evidence to back the claims, prompting more questions from reporters and some members of Congress about the alleged voter fraud.

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“It is the most inappropriate thing for the President to say without proof,” said Republican Senator Lindsey Graham. “He needs to disclose why he believes that. I don’t believe that.”

Spicer repeatedly defended the accusation, saying, “He [Donald Trump] said 3 to 5 million people could have voted illegally based on the studies that he’s seen.”

“We’re talking about a man who won the election and seems to be obsessed with the idea that he could not have possibly lost the popular vote without cheating and fraud,” Graham added.

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However, Senator Mitch McConnell reminded reporters that voter fraud is nothing new.

“It does occur. There’s always arguments on both sides about how much, how frequent and all the rest,” McConnell said. “But most states have done a better job, most states, on this front but the notion that election fraud is a fiction is not true.”

Still, Graham has a message for President Trump: “You’re the leader of the free world and people are going to start doubting you as a person if you keep making accusations against our electoral system without justification. This is going to erode his ability to govern this country if he does not stop it.”

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When asked if the Trump Administration is going to investigate the claims of widespread voter fraud, Spicer simply answered, “Maybe we will.”