A Bloomberg News report first revealed the council's shakeup, quoting a White House official saying that Bannon was originally appointed to monitor former National Security Adviser Michael Flynn, who resigned weeks into his tenure.
Flynn was forced to resign in February over his contacts with Russia's ambassador to the United States, Sergei Kisylak, prior to Trump's taking office on Jan. 20.
The official said Bannon had been placed on the NSC originally as a check on Flynn and had only ever attended one of the NSC's regular meetings.
According to the New York Times, National Security Adviser Lt. Gen. H.R. McMaster was behind the move. McMaster also reportedly restored the Joint Chiefs chairman and intelligence director to the council, while adding the energy secretary, the CIA director and the UN ambassador.
Alongside Bannon's removal, Homeland Security adviser Tom Bossert's role was downgraded, according to a person familiar with the decision and a regulatory finding.
Bannon, Trump's chief strategist and former campaign chief, was appointed to the National Security Council soon after the president took office.
The moved alarmed many in Washington and around the world. The Daily Beast reported on Bannon's "love affair with war," noting that he is an admirer of Lenin and shares his desire to tear down the system.
At the time, Arizona Senator John McCain said the decision was "a radical departure from any national security council in history."
The hashtag #StopPresidentBannon hit the top of Twitter's U.S. trending chart as the site's users began protesting Bannon's newfound influence.
Read more on Steve Bannon: Forget Trump, Bannon is the real danger (Rogel Alpher) | Where is Bannon on the fascism-nationalism spectrum? (Dave Rich)
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