LaMonica McIver

In the year since the Justice Department charged her with assaulting immigration agents outside an ICE detention facility in Newark, Representative LaMonica McIver, Democrat of New Jersey, has tried to present an unflappable face.

“This process has not stopped me from doing my job,” she told supporters outside a New Jersey courthouse in October. “It is not going to stop me from doing my job.”

But the reality is that the case against her by the Trump administration — a test of executive power pitted against a first-term member of Congress who faces the possibility of a 17-year prison sentence — has made it very difficult for Ms. McIver, 39, to carry out her responsibilities.

Her life has been consumed by a case, now playing out in the U.S. Court of Appeals for the Third Circuit, that most of her colleagues and the public have put in the rearview mirror. Yet its outcome could carry major legal implications.