WASHINGTON (AP) — President Donald Trump's former national security adviser Michael Flynn deserves up to six months in prison, the Justice Department said Tuesday, reversing its earlier stance.

Flynn pleaded guilty in 2017 to lying to the FBI about his conversations with the then-Russian ambassador to the United States, including about his request that Russia not escalate tensions with the U.S. in response to sanctions imposed by the Obama administration for election interference.

At the time, he was the closest Trump associate to agree to cooperate in special counsel Robert Mueller's Russia investigation. He met repeatedly with prosecutors over the following months as they investigated whether the Trump campaign coordinated with Russia to sway the election.

He was to have been sentenced in December 2018. But the hearing was upended when a sharp rebuke from a judge raised the prospect that he might send Flynn to prison even though prosecutors hadn't sought that punishment. Flynn asked for the hearing to be postponed so he could continue cooperating with the government in hopes of avoiding prison and proving his value as a witness.

The case has taken a tumultuous turn since then.

The Justice Department opted not to have Flynn testify in the Virginia trial of a former business associate, denying him a chance to be credited for that cooperation.

He also fired his lawyers and replaced them with new ones who have taken a strikingly contentious stance toward Mueller's investigation and accused prosecutors of withholding documents and other information that they said was favorable to Flynn. U.S. District Judge Emmet Sullivan rejected each of the defense arguments in a lengthy opinion earlier this month.

Flynn is one of a half dozen Trump associates charged in the Mueller investigation. All six have either pleaded guilty or been found guilty in a jury trial.

Flynn's lawyers have until Jan. 13 to respond. Sentencing is set for Jan. 28.