Former president Barack Obama warned Donald Trump against hiring Michael Flynn as national security adviser during an Oval Office meeting after the 2016 election, according to three former Obama administration officials.
The information came hours before former acting attorney general Sally Yates was to testify to Congress about concerns she raised to the Trump administration about contacts between Mr Flynn and Russia.
The highly anticipated hearing before a Senate panel investigating Russian interference in the presidential election is Ms Yates's first appearance on Capitol Hill since she was fired.
It is expected to fill in basic details in the chain of events that led to Mr Flynn's ousting in the early weeks of the Trump administration.
Word that Mr Obama directly warned Mr Trump suggests that concern over Mr Flynn's possible appointment spread to the highest level of government months before the official's departure.
The February resignation followed media reports that Mr Flynn had discussed US-imposed sanctions on Russia with Ambassador Sergey Kislyak during the presidential transition period, which was contrary to the public representations of the White House.
Mr Trump moved to distance himself from his former adviser's troubles on Monday, tweeting that it was the Obama administration that gave Mr Flynn "the highest security clearance" when he worked at the Pentagon.
General Flynn was given the highest security clearance by the Obama Administration - but the Fake News seldom likes talking about that.— Donald J. Trump (@realDonaldTrump) May 8, 2017
Mr Trump made no mention of the fact that Mr Flynn was fired by the Obama administration in 2014.
In a second tweet, Mr Trump said Ms Yates should be asked under oath "if she knows how classified information got into the newspapers" soon after she raised concerns about Mr Flynn with White House counsel Don McGahn on January 26.
Ms Yates is expected to testify that she warned Mr McGahn that Mr Flynn's contacts - and the discrepancies between what the White House said happened on the calls and what actually occurred - had left him in a compromised position, according to a person familiar with her expected statements.
White House officials have said publicly that Ms Yates merely wanted to give them a "heads-up" about Mr Flynn's Russian contacts, but Ms Yates is likely to testify that she expressed alarm to the White House about the incidents, according to the person.
Mr Trump has said he has no ties to Russia and is not aware of any involvement by his aides in Moscow's interference in the election.
He has dismissed FBI and congressional investigations into his campaign's possible ties to the election meddling as a "hoax" driven by Democrats bitter over losing the White House.
He has also accused Obama officials of illegally leaking classified information about Mr Flynn's contacts with Mr Kislyak.
Also scheduled to testify is former National Intelligence director James Clapper, who attracted attention for a March television interview in which he said that he had seen no evidence of collusion between the Trump campaign and Russia at the time he left government in January.
Republicans have seized on that statement as vindication for the Trump campaign, but investigations are ongoing.