Machen’s zeal has drawbacks, according to current and former prosecutors. Numerous current and former staff members complained that his intensity wears down subordinates, that he meddles too much in cases and that he doesn’t seem to trust the supervisors who work for him.

Some complained that Machen runs the office like he was a partner at his old law firm, treating employees like associates and pushing them to work outrageous hours while he gets all the glory.

Machen said he sees himself as like a coach — a leader who sets the game plan, picks the players, and bears responsibility for wins and losses. His approach contrasts with that of Jeffrey A. Taylor, a recent U.S. attorney who said in an interview that he saw his role as helping teammates achieve their own successes. Numerous prosecutors have said Taylor was demanding but more trusting of his supervisors than Machen is.

An admirer of President Obama, he donated more than $4,000 to the Illinois Democrat’s various campaigns and worked as a volunteer on the 2008 campaign, helping to vet potential vice presidential candidates.

A spokesman for Machen said the prosecutor would not allow his respect for the president to affect his judgment as he helps lead an investigation into leaks of highly classified information that appeared in news stories.

Those articles highlighted the Obama administration’s active role in clandestine operations against al-Qaeda and other adversaries. Machen and Maryland’s U.S. attorney, Rod J. Rosenstein, were appointed to investigate the matter last week by Attorney General Eric H. Holder Jr. Holder was under pressure from congressional Republicans, who wanted an independent counsel to lead the investigations.

Staff writer Sari Horwitz contributed to this report.