The first few days in any new job are always hard, but Thursday was especially tough for Lindsey Halligan, the newly installed U.S. attorney for the Eastern District of Virginia.

She had to navigate an unfamiliar courthouse, make her first-ever appearance in a criminal case and, on top of all that, indict one of President Trump’s enemies.

Ms. Halligan, who took over on Monday after her predecessor quit rather than prosecute James B. Comey with what he believed was insufficient evidence, had a little trouble with the first two tasks. At one point, she entered the wrong courtroom. When she found the right one, she stood on the wrong side of the judge, then appeared confused about the paperwork she just had signed.

But she accomplished the third task — the one that mattered most to her boss — securing a criminal indictment against Mr. Comey, the former F.B.I. director.

The indictment marked the culmination of an extraordinary series of White House actions that have, in the view of many Justice Department veterans, stripped away remaining legal and procedural restraints that might have prevented Mr. Trump from directing federal law enforcement to humiliate, investigate and prosecute the people he hates.

Mr. Trump’s campaign of retribution began to intensify in mid-July after an adviser stoked his snarling impatience over the slow pace of Justice Department investigations. It hit fever pitch over the past week with the resignation of Erik S. Siebert, the U.S. attorney who believed the evidence against Mr. Comey was insufficient, and with Mr. Trump’s remarkable public demand last Saturday that Attorney General Pam Bondi move quickly to prosecute his enemies.