The former British spy behind a dossier of embarrassing allegations about Donald Trump was "passionate about him not being president", according to a declassified US memo.
The document, commissioned by Republicans on the US House intelligence committee, alleges that ex-MI6 officer Chris Steele was "desperate" for Mr Trump not to win the election.
It also claims that the FBI used unsubstantiated evidence to spy on one of his aides.
Mr Steele reportedly made comments about Mr Trump to then-associate deputy attorney general Bruce Ohr.
"Steele admitted to Ohr his feelings against then-candidate Trump when Steele said he 'was desperate that Donald Trump not get elected and was passionate about him not being president'," the report said.
"This clear evidence of Steele's bias was recorded by Ohr at the time and subsequently in official FBI files - but not reflected in any of the Page FISA applications."
A spokesman for Mr Steele's London-based Orbis Business Intelligence Service said he is not commenting on the allegations.
Mr Trump, who advocated for the memo's release over the fierce objections of the US justice department and the FBI, told reporters the document shows "a lot of people should be ashamed of themselves".
The FBI has said it is inaccurate and missing critical context.
Mr Steele went into hiding after being identified as the author of a report claiming Moscow held incriminating material on the US president-elect which it could use to blackmail him.
The allegations were angrily dismissed as "fake news" by Mr Trump.
Mr Steele is said to have originally compiled the report for political opponents of Mr Trump in Washington.