Ryan and partner Todd Harrison recently went to court to try and prevent investigators from seeing some confiscated files after a raid on Cohen's office and home in April.
It wasn't immediately clear what prompted the change or who would take over. Mr. Cohen wants to hire a lawyer with close ties to the Manhattan U.S. attorney's office, the people said.
A source told the network that the law firm that has been representing Cohen is not expected to work with him going forward.
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Coalition sources said the alliance carried out 18 air strikes on Houthi positions on the outskirts of Al Hudaydah on Wednesday.
Cohen's cooperation would not be welcome news for Trump, his family and others in his inner circle as Cohen has handled some of the commander-in-chief's most sensitive matters, including the $130,000 paid to porn queen Stormy Daniels to keep quiet about her alleged one-night stand with Trump in 2006.
The U.S. Attorney's Office for the Southern District of NY is investigating Cohen for various possible crimes, including potential bank fraud and campaign finance violations.
"Trump should be super anxious about Michael Cohen [flipping]", a former White House official said, noting, "If anyone can blow up Trump, it's him".
"Not a good look and a disaster for Mr. Cohen and Mr. Trump", he said.
Cohen has not yet been contacted by the prosecutors who are conducting the inquiry, said two people briefed on the case.