The February resignation followed media reports that Flynn had discussed USA -imposed sanctions on Russian Federation with Ambassador Sergey Kislyak during the presidential transition period, which was contrary to the public representations of the White House.
Spicer's attacks came a day after Yates told the Senate subcommittee that she had warned the White House that Flynn, also fired by the Obama administration, had misrepresented his contacts with Russian officials and was potentially susceptible to blackmail by Moscow.
Trump's press secretary Sean Spicer said in response that if Obama "was seriously concerned" about Flynn's connections to Russian Federation or other foreign countries, he should have withheld Flynn's security clearance. The president's National Security Advisor, Yates told Team Trump in January, had been compromised. "One of the questions that Mr. McGahn asked me when I went back over the second day", Yates told the senators, "was essentially, why does it matter to [the Justice Department] if one White House official lies to another White House official?"
Congressional committees began investigating after US intelligence agencies concluded that Russian President Vladimir Putin ordered hacking of Democratic political groups to try to sway the election toward Trump.
Yates was joined at the hearing by former Director of National Intelligence James Clapper.
The statements from Yates, an Obama administration holdover, offered by far the most detailed account of the chain of events that led to Flynn's ouster from government in the first weeks of the Trump administration.
He said on Twitter that Yates is a "patriot" for 'defending the Constitution, ' in an apparent reference to her firing after she rejected the Republican president's first travel ban.More news: Verdict expected in blasphemy case against Jakarta's Christian governor
More news: Home's where the heart is for Wiz, Celtics as Game 6 arrives
More news: Former Rep. Brown found guilty in charity scam
"This was a problem because not only did we believe that the Russians knew this but that they likely had proof of this information", she said.
"Ultimately the president made the right decision", Spicer said Tuesday.
"If we want to relitigate the first executive order, at the time, we talked about all of the proper individuals that needed to be made aware of were made aware", Spicer said.
Flynn was not dismissed until 18 days after Yates alerted the White House that the senior aide had lied to the vice president about his conversations with the Russian ambassador in the course of the transition. The White House also tried to impugn Yates' integrity.
Flynn's own contacts with Russia have also raised eyebrows, including an appearance at a 2015 gala for state-sponsored Russian news network RT, during which he was photographed seated next to Russian President Vladimir Putin. "She explained to McGahn the reasons why the DOJ was informing the White House of this - Flynn's conduct was 'problematic in and of itself, ' they believed Pence was entitled to know the information about Flynn he was spreading 'wasn't true, ' and that the American people had been misled about Flynn's actions..."
Monday's testimony came as part of a Senate investigation into Russian meddling in last year's USA presidential election, which Trump won over former Secretary of State Hillary Clinton. "I think that the process worked, frankly, when you look at the time at which we had the information to make the decision that the president made". Was he trying to get a clearer official answer for his superiors? Why?