Donald Trump told a top adviser he wanted to freeze security aid to Ukraine until they helped with investigations into Democrats,
That's according to a New York Times report.
Trump's alleged statement to a then-aide in August was described in an unpublished manuscript by John Bolton - the former national security adviser.
The Times report did not quote Bolton's manuscript but did cite multiple people who described his account.
Bolton's attorney suggested the Times' account was accurate.
The claim may undercut a key part of Trump's defense.
The president argues there was no quid pro quo in a July phone call with Volodymyr Zelensky
in which he asked the Ukrainian President to investigate Joe Biden and his son Hunter Biden.
Joe Biden is a leading contender for the Democratic nomination to oppose Trump in November's election.
Trump was impeached by Congress in December, and is now under trial in the Republican-led Senate.
The Times report puts pressure on Republicans to call Bolton as a witness.
Bolton has said he is willing to testify if the Senate orders him to.
A showdown vote on calling witnesses could come later in the week.