Aide Ousted From White House Re-emerges at Justice Dept.

WASHINGTON — A former American intelligence official who came under intense scrutiny during a stint at the White House last year is returning to government as the national security adviser to Attorney General Jeff Sessions, according to a person familiar with the decision.

The official, Ezra Cohen-Watnick, will play an important role at the Justice Department, advising Mr. Sessions on counterintelligence and counterterrorism.

Mr. Cohen-Watnick is known to be hawkish on Russia and China, believing the intelligence community needs to take a more aggressive approach in countering their activities. Both countries conduct wide-ranging espionage in the United States that targets commercial and government secrets. Mr. Sessions is broadly viewed in the Justice Department as lacking expertise in the area.

The Justice Department declined to comment.

Mr. Cohen-Watnick, 31, served briefly at the start of the Trump administration as the senior director for intelligence for the National Security Council, overseeing covert action and other intelligence programs. He was brought on by Michael T. Flynn, President Trump’s first national security adviser. But some former officials criticized Mr. Cohen-Watnick, a former clandestine officer in the Defense Intelligence Agency, as too young for the job, which is usually filled by C.I.A. veterans.

Mr. Cohen-Watnick was ousted in August 2017 as part of changes in the White House, one of several appointees of Mr. Flynn who were removed by his replacement, Lt. Gen. H.R. McMaster.

National Security Council aides usually draw little public scrutiny, but Mr. Cohen-Watnick was swept up in the tumult of early 2017 when Mr. Trump accused the previous administration, without evidence, of wiretapping his phones at Trump Tower.

Mr. Trump’s allegations were bolstered by Representative Devin Nunes of California, the Republican chairman of the House Intelligence Committee, who said he had evidence that Mr. Trump’s communications were incidentally swept up in surveillance of foreigners by American spy agencies.

Mr. Nunes did not divulge the sources of this information, but American officials later told The New York Times that Mr. Cohen-Watnick, at the instruction of two senior White House officials, helped print intelligence reports that later served as Mr. Nunes’s proof.

The revelation showed that Mr. Nunes and one of the aides, Michael Ellis, a lawyer in the White House Counsel’s Office, were using intelligence to advance political goals. It also undercut Mr. Nunes’s claims that his information came from whistle-blowers, and revealed that he was eager to aid the Trump administration when he was conducting what was supposed to be an independent investigation of Russian election meddling.

Mr. Cohen-Watnick did not provide the intelligence reports to Mr. Nunes.

The episode prompted Mr. Nunes to recuse himself from the committee’s inquiry, which devolved into partisan bickering and has effectively ended.