Federal prosecutors in Washington are facing a decision that will help determine whether Federal Reserve Chair Jerome Powell is swiftly replaced or lingers on while politicians fight over his replacement.

If they do move ahead with a planned appeal against a recent adverse ruling, as U.S. Attorney for the District of Columbia Jeanine Pirro insists they will, they risk having the investigation bogged down in complex, unsettled law, former federal prosecutors with experience in appellate law say.

“Regardless of the procedural vehicle they choose, the substantive road ahead of them is brutally steep,” said Sean P. Murphy, a former assistant U.S. attorney who has argued before the judge who ruled against Pirro’s probe of Powell and has briefed the D.C. Circuit Court of Appeals.

The Trump administration’s plans to quickly confirm former Fed official Kevin Warsh as Powell’s replacement are looking increasingly likely to be a casualty of that legal battle.

Powell in January said the Fed had received subpoenas from Pirro’s office, which he called a pretext to punish him for declining to meet President Donald Trump’s demands to lower interest rates. Later legal proceedings revealed that the subpoenas were related to the cost overruns on Fed building renovations and his testimony about them, matters that Trump has said involve “criminality,” without citing specific evidence.