The special counsel in the Russia investigation is accusing former Trump campaign chairman Paul Manafort of violating his plea agreement by repeatedly lying to federal investigators.
It's an allegation that could expose him to a lengthier prison sentence - and potentially more criminal charges.
The torpedoing of Manafort's plea deal, disclosed in a court filing Monday, also results in special counsel Robert Mueller's team losing a cooperating witness from the top of Donald Trump's presidential campaign who was present for several key episodes under investigation.
That includes a Trump Tower meeting involving Donald Trump Jr. and a Russian lawyer he was told had derogatory information on Democrat Hillary Clinton.
The move signals a return to the acrimonious relationship Manafort has had with the special counsel's office since his indictment last year.
Before his plea agreement, Manafort aggressively challenged the special counsel's legitimacy in court, went through a bitter trial and landed himself in jail after prosecutors discovered he had attempted to tamper with witnesses in his case.
In the latest filing, Mueller's team said Manafort had committed federal crimes by lying about a number of different subject matters even after he agreed to truthfully cooperate with the investigation.
Prosecutors said they will detail the nature of the crimes in writing at a later date to the judge.