In an op-ed for the Wall Street Journal, straightforwardly titled “Kash Patel Doesn’t Belong at the FBI,” Trump’s former national security adviser excoriated Patel for his conduct during the first Trump administration as senior director of the Counterterrorism Directorate for the National Security Council. Bolton went so far as to compare Patel to Soviet dictator Joseph Stalin’s infamous NKVD director, Lavrentiy Beria, who oversaw many of the worst of the regime’s crimes.

“These are but a few of many cases that touch directly on Mr. Patel’s character and his consistent approach of placing obedience to Mr. Trump above other, higher considerations — most important, loyalty to the Constitution,” he wrote after recounting other negative experiences with Patel. “His conduct in Mr. Trump’s first term and thereafter indicates that as FBI director, he would operate according to Lavrentiy Beria’s reported comment to Joseph Stalin: ‘Show me the man, and I’ll show you the crime.’”

Throughout the op-ed, Bolton accused Patel of exaggerating his role in the first Trump administration and of inflating his résumé.

“His puffery was characteristic of the résumé inflation we had detected when Mr. Trump pressed him on us. We found he had exaggerated his role in cases he worked on as a Justice Department lawyer before joining Mr. Nunes’s committee staff,” he wrote. “Given the sensitivity of the NSC’s responsibilities, problems of credibility or reliability would ordinarily disqualify any job applicant.”

Bolton recalled an episode a month before his resignation when two other White House officials, Charles Kupperman and White House counsel Pat Cipollone, were called into the Oval Office to discuss a possible role of Patel as an “administration enforcer of presidential loyalty,” to which the two “strongly objected.”

Bolton’s other objections revolved around previously reported claims from other officials, such as former Defense Secretary Mark Esper’s story about Patel endangering a Navy SEAL mission.

“I regret I didn’t fully discern Mr. Patel’s threat immediately,” Bolton said. “But we are now all fairly warned. Senators won’t escape history’s judgment if they vote to confirm him.”

Bolton has been highly critical of Trump’s Cabinet picks, especially Director of National Intelligence nominee Tulsi Gabbard and former Attorney General nominee Matt Gaetz. He called for the FBI to investigate both last month.

He called Gaetz the “worst Cabinet-level appointment in history,” comparing his nomination to the legend of the Roman emperor Caligula nominating his horse as consul.