Story highlights Trump tweeted that he fired Flynn for lying to Pence and the FBI

Critics are questioning when Trump learned Flynn had lied to the FBI

Washington (CNN) President Donald Trump's tweet on Saturday about firing Michael Flynn from his position as national security adviser is garnering a lot of attention from critics -- with some calling it a possible admission of obstruction of justice.

Trump tweeted about Flynn's Friday guilty plea, in which the former national security adviser said he lied to the FBI about conversations he had with Russian Ambassador to the United States Sergey Kislyak during the transition and disclosed that he is cooperating with special counsel Robert Mueller's office.

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

The tweet immediately caught the attention of critics, who questioned whether Trump knew Flynn had lied to the FBI when the President asked then-FBI Director James Comey to let the investigation into Flynn go.

California Rep. Adam Schiff, the ranking Democrat on the House Intelligence Committee, tweeted, "If that is true, Mr. President, why did you wait so long to fire Flynn? Why did you fail to act until his lies were publicly exposed? And why did you pressure Director Comey to "let this go?"

If that is true, Mr. President, why did you wait so long to fire Flynn? Why did you fail to act until his lies were publicly exposed? And why did you pressure Director Comey to "let this go?" https://t.co/Ea4kOBpWPv — Adam Schiff (@RepAdamSchiff) December 2, 2017