WASHINGTON (CBSNewYork/CBS News) — There’s a new turning point in special counsel Robert Mueller’s investigation into Russian meddling in the 2016 presidential election.

Former National Security Adviser Michael Flynn‘s attorneys have cut ties with the White House.

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CBS News has confirmed via sources familiar with the situation that Flynn’s attorney, Robert Kelner, called Trump lawyer John Dowd on Wednesday night to inform him they could no longer communicate about Flynn, a possible sign that Flynn is ready to cooperate with the investigation.

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Flynn resigned in February after acknowledging secret talks with Russia’s ambassador to the United States.

Trump’s former campaign manager, Corey Lewandowski, says Flynn should be held responsible if he’s guilty.

“If Michael Flynn did something wrong by not disclosing the relationships he had with Turkey and other governments, then he should be held accountable for that,” Lewandowski said on Fox News.

An attorney for President Trump said he assumes Flynn is negotiating a plea deal, but said it doesn’t necessarily have anything to do with the president.

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“It is probably a plea deal,” Jay Sekulow told CBS News. “That is the assumption. And if it is a plea that doesn’t necessarily mean it has anything to do with the president. The Manafort indictment didn’t have anything to do with the campaign or Trump.”

Trump’s legal team has been expecting this development for weeks. They have been awaiting either an indictment of Flynn or his son, or a plea deal involving one of both.

Mr. Trump’s lawyers speculate the charges could revolve around violations of the Foreign Agents Registration Act (FARA). Alternatively, the charges could be connected to Flynn’s advocacy for Turkish entities or his discussions with individuals linked to the Turkish government.

Flynn had a security clearance during Mr. Trump’s campaign and the subsequent transition to the White House as a result of his service as head of the Defense Intelligence Agency. Former President Obama fired Flynn from that position in 2014, but he retained the clearance.

If legitimate, Flynn’s cooperation with the prosecution would give the special counsel investigation insight into the Trump campaign’s operations and the early days of Mr. Trump’s presidency. Flynn’s role within the White House was terminated just 23 days into the Trump presidency.

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CBS News’ Chief White House Correspondent Major Garrett contributed to this report.