Former President Donald Trump returned to a federal courthouse in Washington, D.C. on Tuesday as an appeals court vigorously grilled his lawyers about his claim to be immune from prosecution in his federal election interference case. The former president sat in the courtroom as members of a three-judge panel appeared extremely skeptical of virtually all his lawyers’ arguments, especially one claim that Trump could not be tried because he was not convicted at his Senate impeachment trial after the Jan. 6 attack on the Capitol. “Could a president order SEAL Team Six to assassinate a political ri…