The problem goes beyond credibility and into liability, since he is the lawyer, not Trump, the Lawyer is advising the client on the law, so the lawyer is the responsible one, which through his arrest shows the feds found him either dumb or negligent as a lawyer. It was probably Cohen who advised paying the troll toll (extortion), how it was done was also all on COHEN hence why he was arrested for a mere misdemeanor that everyone one get's away with a mere fine over.
There were more crimes comitted by the feds and the AG and this DA than any they prosecuted Cohen for already. They used intimidation on Cohen to get him to turn and that alone invalidates any cases through obstruction by the corrupt leftist, who by the way can be on the terrorist watch list through their incitement of lawlessness holding NY hostage and in fear aka terrorized. For real in a sane world you instantly deem them terrorist orgs for scheming and designing lawless developement & releases of criminals that are keeping people in fear of going out and living life like normal people.