WASHINGTON (AP) — Democrats' calls for an independent prosecutor to lead the investigation into Trump campaign contacts with Russia grew louder Wednesday in the aftermath of the FBI director's ouster, but the options for an independent probe remain limited, and the only current avenue for such an appointment is in the hands of the Justice Department. The White House has said President Donald Trump's firing of FBI Director James Comey has nothing to do with the ongoing counterintelligence probe, but lawmakers from both parties are questioning the timing and some Democrats also are asking whether Trump's move constitutes interfering in an ongoing investigation. Other alternatives for an independent investigation require congressional approval and, while Democrats are threatening to introduce legislation, a shot at success appears challenging. Democrats also have called for a 9/11-type independent commission and for a select congressional committee to investigate, due to concerns that Republican-led panels may not be motivated to aggressively probe the leader of their party and his campaign. Democrats have been drawing parallels between Comey's firing and President Richard Nixon's "Saturday Night Massacre" firing of the independent special prosecutor overseeing the Watergate investigation in 1973. The last high-profile special counsel to be named was in 2003 when the Bush Justice Department turned to Patrick Fitzgerald, then the top federal prosecutor in Chicago, to investigate who leaked the identity of Valerie Plame, a covert CIA officer. Schumer said Democrats insist a career civil servant at the Justice Department appoint a special counsel to ensure that the American people can have confidence in the criminal justice system. House Minority Leader Nancy Pelosi on Wednesday threatened to use a rarely successful parliamentary maneuver to force a vote on a bill that would create an independent panel to investigate possible contacts between the Trump campaign and Russian officials.