Friends describe Mr. Weissmann as relentless and boundary-grazing but fundamentally fair, a creative legal strategist whose hyperdiligence should not be confused with recklessness.

He is the prosecutor they would want if their relatives were charged with crimes they did not commit, they say, and the one they would dread if their family members were guilty.

“If there’s something to find, he’ll find it,” said Katya Jestin, a former colleague in the United States attorney’s office for the Eastern District of New York, who called Mr. Weissmann’s ethics unimpeachable. “If there’s nothing there, he’s not going to cook something up.”

But many defense lawyers have chafed at what they see as a scorched-earth approach, forged in Brooklyn while facing down Mafia members and refined on the government’s unit of Enron superprosecutors, which left a mixed legacy of high-profile successes, overturned convictions and one unanimous defeat at the Supreme Court.

It was Mr. Weissmann and his team who stunned Houston society by charging the wife of Enron’s chief financial officer with tax fraud, applying pressure on the executive, who became a star witness.

It was Mr. Weissmann, more recently, who oversaw the predawn raid of Mr. Manafort’s Virginia residence in July, when federal agents picked his lock and prosecutors communicated their intention to indict him.

When that moment came this week, representatives for Mr. Manafort and his longtime associate Rick Gates were given little warning: Prosecutors bypassed the common Justice Department practice of inviting lawyers to meet and discuss potential indictments beforehand, often an opportunity for the defense to argue for leniency and for prosecutors to identify potential holes in their case. As of Friday, people close to both men said they had received no indication that an indictment was imminent.