President Trump’s tweet that he fired Michael Flynn for lying to Vice President Mike Pence and the FBI “ups the ante” about what President Trump knew about Flynn’s activities, Maine Sen. Angus King said Sunday.

Speaking on CBS’ “Face The Nation,” King said Trump’s tweet raises new questions about Trump possibly obstructing justice by firing FBI Director James Comey and asking Comey to go easy on Flynn before his dismissal.

“One of the most significant developments is in the last 24 hours where the president tweeted yesterday that he fired [Flynn] because he had lied to the FBI,” King said.

“That's the first time the president has said that. And, it was the next day after he was fired that the president allegedly said to Jim Comey, 'Go easy on Flynn.' If he said to Comey, 'Go easy on Flynn,' knowing that he had lied to the FBI, that ups the ante on that particular part of this whole situation and I think that may be one of the things Mr. Mueller is focusing on.”

Special counsel Robert Mueller charged Flynn with lying to the FBI on Friday and Flynn pleaded guilty to the charge in exchange for his cooperation in the probe.

Flynn was a top campaign adviser to Trump and joined the administration as Trump’s national security adviser. He was fired less than a month into his time in the office for lying to Pence about his conversations with then-Russian Ambassador to the U.S. Sergey Kislyak.