Cohen makes the important point, that while the POTUS may fire USA for no reason at all, "if the attorneys were fired to interfere with a valid prosecution, or to punish them for not misusing their offices, that may well have been illegal."
1. Misrepresentations to Congress. The relevant provision, 18 U.S.C. § 1505, is very broad. It is illegal to lie to Congress, and also to “impede” it in getting information. Deputy Attorney General Paul McNulty indicated to Congress that the White House’s involvement in firing the United States attorneys was minimal, something that Justice Department e-mail messages suggest to be untrue.Cohen sites examples for each violation.
2. Calling the Prosecutors. As part of the Sarbanes-Oxley reforms, Congress passed an extremely broad obstruction of justice provision, 18 U.S.C. § 1512 (c), which applies to anyone who corruptly “obstructs, influences, or impedes any official proceeding, or attempts to do so,” including U.S. attorney investigations.
3. Witness Tampering. 18 U.S.C. § 1512 (b) makes it illegal to intimidate Congressional witnesses. Michael Elston, Mr. McNulty’s chief of staff, contacted one of the fired attorneys, H. E. Cummins, and suggested, according to Mr. Cummins, that if he kept speaking out, there would be retaliation. Mr. Cummins took the call as a threat, and sent an e-mail message to other fired prosecutors warning them of it. Several of them told Congress that if Mr. Elston had placed a similar call to one of their witnesses in a criminal case, they would have opened an investigation of it.
4. Firing the Attorneys. United States attorneys can be fired whenever a president wants, but not, as § 1512 (c) puts it, to corruptly obstruct, influence, or impede an official proceeding.