In the past several months, prosecutors have repeatedly failed to persuade grand juries that the cases they have brought warrant criminal charges. And if it were not unusual enough, they have also been admonished at least three times since last November by federal judges who have accused them of misconduct.

The latest setback came in Chicago, where a judge cited a remarkable list of grand jury errors in a case that was dismissed against four Democratic activists about to face trial for impeding the police during a protest last fall at a suburban immigration detention facility.....

The prosecutors also stacked the deck in their own favor by removing from the panel some grand jurors who had voted against them when considering an earlier version of the charges. Making matters even worse, they tried to hide these maneuvers by redacting the grand jury transcripts — that is, until Judge Perry ordered them to give her the full copies.

The government’s missteps were bad enough to necessitate tossing out the case against the critics of the president’s immigration plan just days before it was supposed to go to trial.....

There are almost no statistics that gauge how often prosecutors fail to secure indictments or are chastised by judges because of their grand jury presentations, if only because such events used to be rare. Legal experts say it is just as uncommon for jurists like Judge Perry to shine a spotlight on grand jury proceedings, which are held in secret, although that, too, has been happening more often.

Barbara L. McQuade, the former U.S. attorney for the Eastern District of Michigan, said that in her 20 years in the Justice Department, she had never worked on a case — or even heard of one — in which a judge had examined grand jury transcripts because of concerns about misconduct.

“Courts almost never do that, mostly because they trust that the government is acting honestly,” Ms. McQuade said. “But if the department demonstrates that it isn’t worthy of that trust, then it invites judges to look under the hood.”....

Part of the problem, legal experts say, is that Mr. Trump has hired inexperienced loyalists to fill senior roles in the Justice Department even as hundreds of career prosecutors have departed — either by their own choice or because they were forced out for having worked on cases that ran afoul of the president.

Junior prosecutors typically attend a weeklong course on the ins and outs of working with grand juries, and often trail more seasoned colleagues before they take the lead in presenting cases. But leaders in politically appointed posts do not get the same kind or amount of training.....

But over the past year or so, there has been a flurry of no true bills in federal courts across the country. Most have occurred in cities like Los Angeles and Washington, where grand jurors have rejected several cases involving people accused of protesting the administration’s immigration crackdowns and surges in federal law enforcement.

Other high-profile failures have involved grand juries hearing cases against Mr. Trump’s political foes — among them, Letitia James, New York’s attorney general, and the six Democratic lawmakers who posted a video reminding military and intelligence personnel of their obligation to disobey illegal orders.