US Vice President Mike Pence has not ruled out an effort to invoke the 25th Amendment, CNN reported.

Pence wants to preserve the option in case President Donald Trump becomes more unstable, a source close to the vice president noted. 

The US Vice President has finally "gotten a glimpse of POTUS's vindictiveness," one source said, using the acronym for President of the United States.

Requesting the 25th Amendment would require Pence and a majority of the Cabinet to vote to remove Trump from office due to his inability to "discharge the powers and duties of his office."