Donald Trump is “strongly considering a full pardon” for Michael Flynn, his first national security adviser who pleaded guilty to lying to the FBI about his dealings with the Russian ambassador before Trump took office.

Flynn cut a deal as part of special counsel Robert Mueller’s investigation of Russian election interference and links between Trump and Moscow.

He initially cooperated with the investigation, which concluded last year without establishing criminal conspiracy but did lay out extensive evidence of contact between Trump aides and Russia and possible obstruction of justice by the president himself.

Flynn, who was fired as national security adviser after only 24 days in the role, has not yet been sentenced but a number of Trump aides and associates have been convicted and jailed in cases arising from Mueller’s work.

Flynn faces possible prison time.

He sought to withdraw his guilty plea in January, “because of the government’s bad faith, vindictiveness and breach of the plea agreement”.

His change in tack came after he hired a new lawyer, Fox News pundit Sidney Powell, a longtime critic of the Mueller inquiry who has peddled numerous false conspiracy theories on the investigation and other Trump policies and issues in prime time interviews.

On Sunday, Trump tweeted: “So now it is reported that, after destroying his life & the life of his wonderful family (and many others also), the FBI, working in conjunction with the Justice Department, has ‘lost’ the records of General Michael Flynn. How convenient.

“I am strongly considering a Full Pardon!”

Although Trump did not cite specific reports, Powell had tweeted hours earlier an unsubstantiated claim that “#FBI still hiding evidence of #Flynn‘s innocence”.

Powell, who has also repeatedly retweeted antisemitic conspiracy theories, has contended in rambling legal filings that FBI officials altered an interview summary with Flynn and conspired to prevent him from obtaining legal counsel before he was interviewed.

Trump’s use of the presidential pardon power has proved vastly controversial, as he has commuted sentences or pardoned prominent supporters including former sheriff Joe Arpaio and former New York City police commissioner Bernie Kerik.

In cases related to the Russia investigation, Trump has flirted with the notion of pardoning or granting clemency to Paul Manafort, his former campaign chair who was found guilty of financial charges, and to Roger Stone, a longtime ally who was found guilty of lying to Congress and tampering with a witness.

“Somebody has to stick up for the people,” Trump said in February.