In the three weeks since President Trump flooded the streets of Washington with hundreds of troops and federal agents, there have been only a few scattered protests and scarcely a word from Congress, which has quietly gone along with the deployment.

But one show of resistance has come from an extraordinary source: federal grand jurors.

In what could be read as a citizens’ revolt, ordinary people serving on grand juries have repeatedly refused in recent days to indict their fellow residents who became entangled in either the president’s immigration crackdown or his more recent show of force. It has happened in at least seven cases — including three times for the same defendant.

Given the secretive nature of grand juries, it is all but impossible to know precisely why this has been happening, but the persistent rejections suggest that grand jurors may have had enough of prosecutors seeking harsh charges in a highly politicized environment.

Courthouse wits have long quoted Judge Sol Wachtler, the former New York jurist who said that prosecutors are in such complete control of grand juries that they could get them to indict a ham sandwich. But that old saw did not hold true in the rebellion in Federal District Court in Washington, where grand jurors seem to have taken a stand in defense of their community.

“First of all, it is exceedingly rare for any grand jury to reject a proposed indictment because ordinarily prosecutors use discretion in only bringing cases that are strong and advance the interests of justice,” said Barbara L. McQuade, a former U.S. attorney in Detroit who teaches at the University of Michigan Law School. “I have seen this maybe once or twice in my career of 20 years, but this is something different.”

“My guess,” Ms. McQuade went on, “is that these grand jurors are seeing prosecutorial overreach and they don’t want to be part of it.”