White House Chief Strategist Steve Bannon listens at right as President Donald Trump speaks during a meeting on cyber security in the Roosevelt Room of the White House in Washington, Tuesday, Jan. 31, 2017. Evan Vucci AP
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Bannon is also joining mega donor Robert Mercer, co-CEO of the investment management company Renaissance Technologies, and his daughter, Rebekah, in a new venture, perhaps on a new outside group, according to a former Trump campaign staffer who was in touch with him Friday.

Breitbart, founded in 2007, already has been extremely critical of some White House aides in recent weeks. McMaster has been the subject of numerous stories accusing him of being hostile to Israel, promising former Obama aide Susan Rice she could keep her security clearance and linking him to billionaire George Soros, a wealthy supporter of liberal causes.

Scott Jennings, a Republican strategist who worked for George W. Bush and is close to people in the Trump White House, said the problem wouldn’t be what Bannon writes about the White House — but rather how Trump reacts to what he writes.

“How is the president going to react to ramped up criticism of his remaining advisers?” Jennings asked. “He is affected by what he sees or what he reads. It doesn’t really matter what Breitbart writes unless the president is affected by it.”

The undisciplined president could take to Twitter, which he does nearly daily, to lash out at anyone who criticizes him or respond by firing more staffers.

Another Republican close to the White House said Bannon won’t win if he attempts to attack the administration.

“If Bannon attempts an assassination campaign against White House staffers he considers are globalists and his America First policies over trade, immigration and national security, it could backfire big time,” the person said. “The president sides with his team being attacked from either within or outside the Oval Office and (that's) what contributed to Bannon’s ouster.”

Vera Bergengruen contributed reporting.