General Flynn sought mandamus relief before the United States Court of Appeals for the DC Circuit. DC Circuit rules speak to mandamus procedures. Specifically, Rule 21(b)(4) states:
The court of appeals may invite or order the trial-court judge to address the petition or may invite an amicus curiae to do so. The trial-court judge may request permission to address the petition but may not do so unless invited or ordered to do so by the court of appeals.
So what is the upshot? The mandamus applicant (ie, Flynn) is asking the court of appeals to stop Judge Sullivan (ie, the trial court judge) from appointing an amicus. Flynn’s position is that Judge Sullivan lacks the authority to appoint an amicus in his criminal proceeding—a position that Judge Sullivan apparently adhered to in earlier stages in this very case. Unlike the trial court, the court of appeals, under its appellate rules, has the express power to appoint amici (even in a criminal matter). The amici before the court of appeals may very well opine that the trial court erred in appointing an amicus.
I suspect that this will not end well for the reputation of the federal courts.
Currently, the country waits for the court of appeals to issue a briefing schedule order.
Seth Barrett Tillman, General Flynn & Amici in the Federal Courts, New Reform Club (May 21, 2020, 7:48 AM), <https://reformclub.blogspot.com/2020/05/general-flynn-amici-in-federal-courts.html>;