A source close to President Donald Trump said the latest developments surrounding his former national security advisor Michael Flynn are "very, very, very bad," according to NBC News.
Flynn pleaded guilty on Friday to lying to the FBI and agreed to cooperate with investigators working on special counsel Robert Mueller's Russia probe.
As part of Flynn's plea deal he agreed to "cooperate fully, truthfully, completely, and forthrightly" with the special counsel's office. His cooperation could include taking government-administered polygraph tests and participating in covert operations, according to the agreement.
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Flynn is the first Trump White House official to be charged with a crime in connection to Mueller's investigation.
Flynn's plea is "a very big deal," said Gerald Lefcourt, a leading criminal defense attorney.
Lefcourt, a past president of the National Association of Criminal Defense Lawyers, said it signals that Mueller believes information from Flynn will be used to successfully prosecute other Trump associates.
Ty Cobb, an attorney for the president, signaled that he remained optimistic about the president's prospects with regard to the probe.
Trump has repeatedly denied any inappropriate connections between his aides and the Russian government.
Cobb didn't respond to a request for comment from CNBC. A spokesperson for the White House also did not immediately respond.
— CNBC's Dan Mangan contributed to this article.