Sen. Roy Blunt Roy Dean BluntSocial media platforms put muscle into National Voter Registration Day Senate GOP faces pivotal moment on pick for Supreme Court This week: Supreme Court fight over Ginsburg's seat upends Congress's agenda MORE (R-Mo.) said Sunday that President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE's former personal attorney allegedly lying to a congressional committee is a "big mistake" and he's glad special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE is taking it "seriously."

"I certainly do think that lying to the [Senate] Intelligence Committee, which I am a part of, is a big mistake for whoever does it and creates lots of problems for the committee itself," Blunt told "Fox News Sunday," adding that one lie can throw off an entire investigation and waste hours of work. The Senate Intelligence Committee has investigated Russian interference in the 2016 election.

"I’m glad to see the special prosecutor seeing that particular crime seriously," he added.

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Cohen pleaded guilty last week to making misstatements to Congress while testifying about his contacts with Russians during the 2016 presidential campaign.

He also agreed to cooperate with Mueller's investigation, according to a plea deal released by the special counsel.

The president called Cohen a "weak person" following the reports that he had pleaded guilty and accused him of "lying" in order to reduce his punishment.

“He’s trying to get a much lesser sentence by making up the story,” Trump said, adding “everybody knows about this deal.”



Cohen pleaded guilty to various federal crimes in August, including campaign finance violations, which Cohen has suggested he did with Trump's knowledge.

Trump has denied this was the case and Cohen's attorney Lanny Davis, an opinion contributor to The Hill, also told MSNBC in August that there may be independent evidence outside of Cohen's word that the president violated campaign finance law.