Making her first public statements about the issue, Yates said she feared Moscow could try to blackmail Flynn because it also knew he had not been truthful about conversations he had with Ambassador Sergei Kislyak about US sanctions on Russian Federation.
It was Yates who first alerted the White House in January that Flynn had lied to administration officials, including Vice President Mike Pence, about his communications with Russian Ambassador Sergey Kislyak, and who warned that Flynn might be vulnerable to blackmail by the Russians. It was nominally about Russian interference in the 2016 election, including concerns that the Russian government could have compromised Flynn - concerns Yates raised with McGahn during Trump's first week in office.
"The national security adviser could be blackmailed by the Russians", Yates told a Senate subcommittee that was largely divided along partisan lines.
The Associated Press meanwhile reported last week that one sign taken as a warning by Obama administration officials about Flynn's contacts with Kislyak was a request by a member of Trump's own transition team made to national security officials in the Obama White House for the classified Central Intelligence Agency profile of Kislyak.
However, it took 18 days from the second meeting - and only after the news was leaked and published by the Washington Post - for the White House to fire Flynn.
In tweets on Monday, Mr Trump doubled down on that stance.
"Trump tweeted that there is "no evidence" of collusion between himself and Russian Federation, that Yates didn't reveal anything new during her testimony, that the investigation into collusion between Russian Federation and Trump is a "total hoax", and that the media should be reporting on surveillance instead, finishing off the string of tweets with the hashtag, "#FakeNews!".
The president also said the "biggest story" to emerge on Monday "is on surveillance. Why doesn't the media report on this?" he asked.
Trump was told personally, by a man who has yet to be busted by the press for a lie anywhere near the level that Trump achieves on a daily basis, not to hire Flynn. Graham told them he intends to find out.
Obama aides also described Flynn as notably dismissive of the threat Russian Federation posed to the United States when discussing policy in transition meetings with outgoing national security adviser Susan Rice and other top officials.
"They are attuned, it seems, more to defending the president than to taking care of national security business in an appropriate way", Whitehouse said. "I don't know what the Federal Bureau of Investigation knows".
Now there are calls among Democrats in her home state of Georgia for Yates to become a candidate, possibly for governor next year.
"We're not going to relitigate the past on this", Spicer said. Ted Cruz's attempted grilling of Yates at Monday's hearing seem so unusual.
Yates, known as a tough and independent prosecutor, has been a target of Trump's ire since he fired her at the end of January for refusing to support his controversial immigration ban on nationals from six Muslim majority nations.
Clapper stood by his earlier statement that he is not aware of evidence indicating any such collusion.