The terms of the plea agreement waive any right to retract Manafort's guilty pleas, so he's on the hook no matter what.
Trump has consistently called the Mueller probe a "witch hunt" and strongly denies any collusion with Russian Federation in the 2016 presidential election.
The president described Mueller as "only looking at one side and not the other" and said his team is "ruining lives for them refusing to lie".
Mueller also noted that the guilty pleas stand as a result, while an agreement by prosecutors to a reduced sentence based on cooperation was no longer required. It indicates that not only did Manafort speak extensively with the Justice Department prosecutors for their investigation, but they also believe they were able to verify or refute information he gave them.
"It seems to me he's angling for the pardon", said David Weinstein, a former federal prosecutor in Miami.
Trump called Mueller the "exact opposite" of a saint who is doing "TREMENDOUS" damage to the country's criminal justice system by probing Russian interference in the 2016 election. Look at their past, and look where they come from. Let these bad people go back to the Clinton Foundation and "Justice" Department!
A jury found Manafort guilty of eight of 18 counts of tax and bank fraud in a federal trial in NY on August 21.
Ukraine and Russian Federation in naval standoff near Crimea bridge
The worldwide community has largely not recognized Russia's annexation of the Black Sea peninsula of Crimea from Ukraine. Ukraine's foreign ministry said in a statement it wanted a clear response to the incident from the worldwide community.
Of course this is all just speculation, and perhaps Manafort has other reasons for allegedly lying to investigators.
"The consequences are potentially devastating for Manafort", said Washington attorney Shanlon Wu, who represented Manafort's former associate Rick Gates before he pleaded guilty and became a star witness for prosecutors in Manafort's Virginia trial.
Manafort said in the same filing on Monday that he disagreed with Special Counsel Robert Mueller's assertion that he had lied, but both sides agreed the court should move ahead and sentence him for his crimes.
Mueller said in the filing that after signing the plea agreement "Manafort committed federal crimes by lying to the Federal Bureau of Investigation and the Special Counsel's Office on a variety of subject matters".
"I view this as bad news for Mueller, as well as Manafort, since it means Mueller can not use Manafort to testify against anyone else", said Seth Taube, a former federal prosecutor. "You can expect the judge, who has already had some harsh words for Manafort when he violated his bond conditions, tot are this conduct into account at sentencing". He remains jailed while awaiting his sentence.
Earlier Monday, former Trump campaign foreign policy adviser George Papadopoulos reported to a prison in Wisconsin to serve a 14-day sentence for lying to investigators.