Earlier quoted context omitted.
"Although the attorney general advises the president, the basic authority of the office is derived from Congress and the functions of the office are subject to congressional control. In addition, the attorney general is a member of the bar and therefore an officer of the court subject to the directives of the judicial branch." - http://legal-dictionary.thefreedictionary.com/Attorney+Gener...
"the attorney general is a member of the bar" While I'm sure that's always or virtually always been true in practice, nothing in the relevant U.S. Code appears to require it (it is definitely not the case for the Supreme Court).
And there are no legal guidelines to whether you are allowed to be a federal judge of any kind. The same is not true of prosecutors.