Flynn was the first member of Trump's administration to plead guilty to a crime uncovered by Mueller's wide-ranging investigation into Russian attempts to influence the 2016 US presidential election and possible collusion by Trump aides.
In related news, former FBI Director James Comey has also faced scrutiny for knowing the import of former Attorney General Loretta Lynch's meeting with Bill Clinton during Hillary Clinton's presidential campaign, but deceiving the public about the "matter".
The White House did not immediately respond to a request for comment on Trump's tweet. "No collusion. There's been absolutely - there's been absolutely no collusion, so we're very happy", Trump told reporters Saturday morning before departing for a fundraising trip to NY.
Prior to his tweet, Trump had said that he dismissed Flynn for lying to Pence, but this is the first time he had said anything in regards to Flynn lying to the Federal Bureau of Investigation.
Flynn also admitted that he spoke with another member of the transition team before he talked to Kislyak about USA sanctions on December 29, court records say.
"Far too many questions still remain unanswered about the Trump Russia scandal, such as who was involved with instructing Flynn to speak with the Russians directly, about what, and why", said Rep. Eliot L. Engel, D-N.Y., top Democrat on the House Foreign Affairs committee. No collusion. There's been absolutely, absolutely no collusion, so we're very happy.
According to new court documents, Flynn was in contact with senior Trump transition team officials at Mar-a-Lago about conversations with then-Russian Ambassador Sergey Kislyak regarding U.S. sanctions on Russia. At this point, the only person who knows whether Brian Ross's report is accurate is Michael Flynn. Afterward, Comey said that Trump had asked him to drop the investigation into Flynn.
At the time of Flynn's dismissal, the White House acknowledged only that Flynn had lied to Vice President Mike Pence about what he discussed with the ambassador - sanctions imposed by then-president Barack Obama against Russian Federation for meddling in the election.
A few hours later, Mr. Strzok and his team were back in Mr. Comey's conference room for a final briefing: Only about 3,000 emails had been potentially work-related.
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"There is not a legal issue but rather a trust issue", then-White House press secretary Spicer said at the time.