When he was named special counsel in May, Robert S. Mueller III was hailed as the ideal lawman — deeply experienced, strait-laced and nonpartisan — to investigate whether President Trump’s campaign had helped with Russian meddling in the 2016 presidential election.

The accolades squared with Mueller’s valor as a Marine rifle platoon commander in Vietnam and his integrity as a federal prosecutor, senior Justice Department official and FBI director from 2001 to 2013 — the longest tenure since J. Edgar Hoover’s. He was praised by former courtroom allies and opponents, and by Democrats and Republicans in Congress.



For the record: An earlier version of this article incorrectly spelled the last name of East German physicist and spy Alfred Zehe as Zehle. It also said Mueller was 50 when he returned to private practice in 1993; he was 49 at the time.

But at 73, Mueller has a record that shows a man of fallible judgment who can be slow to alter his chosen course. At times, he has intimidated or provoked resentment among subordinates. And his tenacious yet linear approach to evaluating evidence led him to fumble the biggest U.S. terrorism investigation since 9/11.