The hearing took place hours after former Obama administration officials revealed that the outgoing president had warned Mr Trump against hiring Mr Flynn during an Oval Office meeting after the 2016 election. Trump surrogates such as KellyAnne Conway initially responded by saying Flynn's job was safe, and only when the backlash proved Flynn's position was untenable did Flynn get fired, with Trump praising him and criticizing the media as Flynn left.
Yates, appearing before a Senate panel investigating Russian interference in the election, described discussions with Don McGahn, the Trump White House counsel, in which she warned that Flynn apparently had misled the administration about his communications with Sergey Kislyak, the Russian ambassador.
Yates testified she and a senior official in the national security division at the Justice Department met with McGahn, the top White House lawyer, on two consecutive days a week after the inauguration at the White House to discuss statements by Flynn and others "that we knew not to be the truth".
As Sen. Richard Blumenthal, D-Conn., said to Yates, "Without that published report, and without the free press telling us a lot of what went on, Michael Flynn might still be sitting in the White House as national security adviser, because by January 30th, you were forced to resign, correct?"
Commenting on this conversation on Fox news, President Donald Trump blamed the Obama administration for not vetting Flynn. She said she was not sure what the White House had done after she left.
Spicer added that he was not aware of any security restrictions placed on Flynn after the warning.
On Jan. 26, Yates said, she called the White House counsel, Donald F. McGahn II, regarding "a very sensitive matter" that they could discuss only in person. The message was part of a series of late-night tweets about the testimony of former Acting Attorney General Sally Yates and the investigation as a whole.
Vice President Pence had initially said that Flynn and the ambassador did not discuss USA sanctions against Russian Federation, which turned out not to be true. James Clapper, director of national intelligence under Obama, also testified Monday. Richard Blumenthal, D-Conn., said that if the information had never been made public, "Michael Flynn might still be sitting in the White House as national security adviser".
Spicer said that Trump defended Flynn after the White House learned that he lied because he is "somebody who served our country honorably in uniform for over 30 years".
Donald Trump has been accused of trying to intimidate a witness who was set to testify at a hearing about possible Russian interference in the U.S. election.
The Senate now in the middle of an investigation into the potential ties between Donald Trump's campaign and Russian operatives, so to add extra emphasis to his claims that there was no collusion, the president temporarily changed his Twitter header image to one of his tweets about the case.
Spicer said that after the White House first viewed the evidence and materials on February 2, which were first flagged by Yates on January 26, there were various meetings and discussions that took place leading up to the request for Flynn's resignation on February 13.
"But also more importantly, for the discussion today about Russian Federation, [she was] really laying out that this was just not a heads-up she gave the White House".
"Kind of a stretch", he said of Yates' claim. Obama himself told one of his closest advisers that the Federal Bureau of Investigation, which by then had been investigating Trump associates' possible ties to Russian Federation for about six months, seemed particularly focused on Flynn.