"Michael Cohen's an idiot. To be taping — if he did tape — conversations with his client, that's stupid," Graham said on "The Brian Kilmeade Show."
"I don't know what kind of legal advice Michael Cohen gave Donald Trump. I'm not really impressed with him as a lawyer, just to be honest with you," he added.
The FBI raided the offices and hotel room of Cohen on Monday. The Justice Department confirmed on Friday that he is part of a criminal investigation. 
ABC News reported that recordings by Cohen — who was known to occasionally tape conversations with others — were seized during the FBI raids.
But, according to the Times, Cohen has privately said he did not make recordings of his conversations with Trump. The president's team has separately argued that records seized by the FBI are protected by attorney-client privilege.
Though Trump and Cohen spoke on Friday, White House press secretary Sarah Huckabee Sanders said she was "not sure" if Cohen was still Trump's personal lawyer.