But Graham sent Mueller a letter late last week asking if he wanted to testify about "any misrepresentation" of a call between the special counsel and Barr that took place after the attorney general released his four-page memo outlining the key findings of Mueller's Russia probe.

A spokeswoman for Graham said on Wednesday that they had not heard back from Mueller or his team in response to the letter.

Mueller sent Barr a letter shortly after he released the memo in late March saying it did not "fully capture the context, nature and substance of this office's work and conclusions." Barr, during his testimony last week, defended his actions, saying Mueller's concerns were not about the letter but the media coverage surrounding it.