President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE in an early morning tweet on Tuesday wished Michael Flynn good luck ahead of his first national security adviser's sentencing for lying to the FBI.

"Good luck today in court to General Michael Flynn," the president said. "Will be interesting to see what he has to say, despite tremendous pressure being put on him, about Russian Collusion in our great and, obviously, highly successful political campaign. There was no Collusion!"

Good luck today in court to General Michael Flynn. Will be interesting to see what he has to say, despite tremendous pressure being put on him, about Russian Collusion in our great and, obviously, highly successful political campaign. There was no Collusion! — Donald J. Trump (@realDonaldTrump) December 18, 2018

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Flynn, who will appear in D.C. federal court before U.S. District Judge Emmet Sullivan later Tuesday, pleaded guilty to one count of making false statements last December.

Special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE has recommended a lenient sentence, citing Flynn's "substantial assistance" in ongoing investigations, and has not asked for any jail time.

The president and his allies have cast Flynn as a victim of overreach on Mueller’s part, claiming the former Trump campaign surrogate did nothing wrong and was pressured to lie.

It was reported on Monday, however, that associates of Flynn are being charged with illegally lobbying for the extradition of a U.S.-based Turkish dissident.

Flynn came under scrutiny after writing an op-ed in The Hill newspaper on Election Day 2016 in which he defended Turkish President Recep Tayyip Erdoğan amid growing concerns over a crackdown on dissidents.

Flynn’s hearing Tuesday comes amid a flurry of activity from Mueller’s office. Former Trump attorney and fixer Michael Cohen was sentenced last week to three years in prison on a slew of charges, including two campaign finance violations in which he implicated the president.

--Tal Axelrod contributed to this report, which was updated at 7:19 a.m.