Washington (CNN) Former White House chief strategist Steve Bannon has privately confided that he believes President Donald Trump only has a 30% chance of completing his full term, a source told Vanity Fair.

According to two of Vanity Fair's sources with knowledge of the conversation, Bannon warned Trump several months ago that the biggest threat to his presidency is not impeachment by Congress, but the 25th Amendment -- which could allow his Cabinet to vote to remove him.

CNN has been unable to independently confirm these reported conversations. Bannon could not be reached for comment.

The 25th Amendment to the Constitution is a measure that establishes a system for replacing the president or vice president in case there is a death, removal, resignation or incapacitation.

Also, if the vice president "and a majority of either the principal officers of the executive departments or of such other body as Congress may by law provide" make a "written declaration that the president is unable to discharge the powers and duties of his office, the vice president shall immediately assume the powers and duties of the office as acting president."

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