Sen. Angus King Angus KingGovernment watchdog recommends creation of White House cyber director position Democrats step up hardball tactics as Supreme Court fight heats up Shakespeare Theatre Company goes virtual for 'Will on the Hill...or Won't They?' MORE (I-Maine) on Tuesday said he's "not prepared to reach" the conclusion that President Trump obstructed justice by urging former FBI Director James Comey to end his agency's investigation into former national security adviser Michael Flynn.

But King said the president's alleged request raises questions after a tweet from Trump's account over the weekend claimed that he fired Flynn because he knew Flynn lied to the FBI.

In an appearance on CNN, King said he was not ready to go that far when asked if Trump's actions constituted obstruction of Justice.

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"I'm not prepared to reach that conclusion, but certainly the tweet over the weekend ... I think that's a serious question," said King, who sits on the Senate Intelligence Committee, one of the congressional panels investigating Russia's role in the 2016 election.

The discussion about Trump's decision to fire Flynn in February re-emerged a day after the former national security adviser pleaded guilty to lying to the FBI about his contacts with Russian Ambassador Sergey Kislyak in the month before Trump took office.

Flynn was ousted just 25 days into office after it was revealed that he lied to Vice President Pence and others about the conversations. At the time, Trump said it was because Flynn misled Pence that he fired him.

But in a Saturday tweet, Trump said, "I had to fire General Flynn because he lied to the Vice President and the FBI. He has pled guilty to those lies. It is a shame because his actions during the transition were lawful. There was nothing to hide!"

John Dowd, a lawyer for Trump, later took responsibility for the tweet from the president's personal Twitter account.

But CNN reported Monday that White House counsel Don McGahn told Trump in January that he believed Flynn may have lied to the FBI and should be fired. Flynn did not leave the White House until Feb. 13.

Whether Trump obstructed justice is being looked at as part of special counsel Robert Mueller's investigation into Russian meddling in the 2016 election and possible collusion between the Trump campaign and Moscow.

Trump has denied any coordination between his campaign and Russia, and has called Mueller's investigation a "witch hunt."

Dowd has also claimed in recent days that Trump, as the president, cannot technically obstruct justice, because he is the nation's top law enforcement official.