Kash Patel defended his tenure as FBI director before a US Senate panel, angrily pushing back on questions about his handling of the Jeffrey Epstein case and the firings of veteran officials.
Mr Patel's appearance before the Senate Judiciary Committee came as critics, including some allies of President Donald Trump, have questioned his leadership of the most prominent US law enforcement agency.
The FBI director offered a broad defence of his tenure, touting what he said was an increase in FBI arrests for violent crime and seizures of illegal guns.
Senator Dick Durbin, the ranking Democrat on the Senate Judiciary Committee, accused Mr Patel of inflicting "untold damage on the FBI" and putting national security and public safety at risk with an "unprecedented purge of FBI officials".
Democratic Senator Cory Booker said the mass firings of FBI agents who worked on past criminal cases brought against Mr Trump had "made our country weaker and less safe" and predicted the FBI chief is "not going to be around long".
"As much as you supplicate yourself to the will of Donald Trump - and not the Constitution of the United States of America - Donald Trump has shown us... he is not loyal to people like you. He will cut you loose," Mr Booker said.
Pressed by Democratic Senator Adam Schiff as to whether any FBI agents had been fired in political retribution, Mr Patel erupted, calling the California lawmaker the "biggest fraud to ever sit in the United States Senate" and a "political buffoon".
"I do not have an enemies list," Mr Patel said.
"The only actions we take, generally speaking, for personnel at the FBI are ones based on merit and qualification and your ability to uphold your constitutional duty. You fall short, you don't work there anymore."
Mr Patel has pushed to align the FBI, which has traditionally sought to insulate its investigations from political influence, more closely with Donald Trump and his agenda.
The FBI during Mr Trump’s second term has removed scores of senior officials, including those with deep experience countering national security threats.
Three other former senior FBI officials, including a former acting director, sued last week claiming they were fired for being insufficiently loyal to Mr Trump.
The lawsuit alleges that Mr Patel said privately that his job depended on expelling officials who had been involved in investigations into Mr Trump, who faced two now-dismissed federal criminal cases during his years out of office.
Senators also questioned Mr Patel about the Justice Department’s decision, revealed in an unsigned memo in July, not to release additional materials related to its investigation of Epstein, a wealthy financier and convicted sex offender who died by suicide while awaiting trial on sex trafficking charges.
The determination touched off a political crisis for Mr Trump, enraging many online right-wing supporters who expected his administration to reveal details about other wealthy and powerful people with connections to Epstein.
It also cast renewed scrutiny on Mr Trump’s prior friendship with Epstein, who had been accused of sexually abusing underage girls.
Mr Trump has not been accused of misconduct.
Mr Patel said there is no "credible information" in the law enforcement files he has seen that Epstein trafficked young women to other individuals.
"There is no credible information, none," Mr Patel said. "If there were I would bring the case yesterday that he trafficked to other individuals."
Mr Patel sought to deflect blame to a federal investigation into Epstein run out of Florida beginning in 2004, saying the US attorney in charge of that probe improperly narrowed its scope.
That explanation was not mentioned in the Justice Department's July memo.
