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.
"To state the obvious, you don't want your national security adviser compromised with the Russians", Yates said Monday.
Senate lawmakers also asked Yates and Former National Intelligence Director James Clapper if they had ever reviewed classified documents in which names of Trump's associates were unmasked.
She said she was giving the information to the Trump White House so that they could take "the action that they deemed appropriate" and that she believed the Russians already knew that Flynn had misled administration officials. Graham asked both Clapper and Yates if they are aware of any evidence that anybody in the Trump campaign "colluded with the Russian government intelligence service in improper fashion".
The revelation came as former acting Attorney General Sally Yates testified for the first time in public before a congressional panel about Mr Flynn's contacts with Mr Kislyak. She reminded him, "That's what I promised you I would do, and that's what I did". Trump made no mention of the fact that Flynn had been fired by the Obama administration in 2014. Spicer said. "There were steps that they could have taken that - if that was truly a concern".
Mr Flynn's links to Russian Federation are being scrutinised by the FBI and the House and Senate Intelligence Committees, as part of wider investigations into claimsMoscow sought to tip the election in favour of Mr Trump, and into contacts between Russian Federation and members of the president's campaign team.
Clapper confirmed that British intelligence officials shared "very sensitive" information about Russian connections to Trump's campaign.
"The efforts by a foreign adversary to interfere and undermine our democratic processes - and those of our allies - pose a serious threat to all Americans", Yates said. The national security adviser was let go 18 days after Yates first raised her concerns with White House counsel Don McGahn.
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Trump did not, however, pay heed to Obama's counsel on Flynn, bringing aboard the former military intelligence officer who supported Trump during his campaign as his National Security Advisor.
"President Donald Trump called Clapper's comments a full dismissal of potential collusion and dismissed the entire issue outright in the series of tweets after the hearing, referring to information from the day's events as "old news", "a total hoax" and "#FakeNews!".
But President Donald Trump did not immediately fire the adviser, Michael T. Flynn, over the apparent lie or the susceptibility to blackmail.
Ms Yates was appointed by the Obama administration and was sacked by Mr Trump on January 30 for refusing to defend his travel ban. Billingslea knew Flynn would be speaking to Kislyak, according to two former Obama administration officials, and seemed concerned Flynn did not fully understand he was dealing with a man rumored to have ties to Russian intelligence agencies.
In the almost three weeks that passed between finding out Flynn misled the Vice President Mike Pence about his contacts with Russia's ambassador to the USA and Flynn's resignation, Spicer said, there were no known restrictions to his access to information.
While it appeared to have little effect on the French election's outcome, it paralleled the leak of Democratic party files past year ahead of the U.S. vote, which hurt Clinton and boosted Trump.
Yates sidestepped questions about the FBI's investigation of Trump's campaign and Russian Federation.
"Ms. [Nicole] Meyer wanted to make clear that her brother had stepped away from the company in January and has nothing to do with this project", the company said in a statement.