"You don't really care about Mr Manafort's bank fraud", Judge TS Ellis said.
It's a significant milestone for the probe, which began exactly two years ago as an Federal Bureau of Investigation counterintelligence inquiry into Russian interference in the 2016 presidential election.
Manafort was present during the June 2016 Trump Tower meeting that was set up after a Kremlin-linked lawyer offered up dirt on Democratic nominee Hillary Clinton to members of the Trump campaign.
"Wow, what a tough sentence for Paul Manafort, who has represented Ronald Reagan, Bob Dole and many other top political people and campaigns", Trump tweeted on June 15. But none of the cases stemming from Mueller's probe have gone to a jury trial - until now.
Prosecutors are expected to argue that Manafort's lavish spending on suits, homes and luxury items did not match the income declared on his tax returns and that he misled lenders when he borrowed tens of millions of dollars against NY real estate.
Those questions will be answered by 12 jurors selected this week as Manafort's trial on tax evasion and bank fraud charges gets underway at the courthouse in Alexandria, Virginia. He has pleaded not guilty to those charges. While scrutiny of the Ukraine dealings pushed the one-time campaign chairman out, Gates stayed on, serving as a liaison to the Republican National Committee, while earning the reputation of a competent executor of the Trump team's day-to-day operations.
Manafort remained defiant, vowing to fight the charges. They argued in one court filing that Mueller's office overstepped its authority by producing indictments that focused on details having "no connection to coordination between the Russian government and the Trump campaign". "With a northern Virginia jury, they know they may not be kindly disposed to the president".
The heart of the government's case involves nine years of Manafort's lucrative lobbying and consulting for Ukraine and its former leader Victor Yanukovych, work the USA government said Manafort should have registered with the Justice Department.
Rudy Giuliani, the president's personal lawyer, has indicated that Mr Trump could pardon Mr Manafort should he be found guilty. Trump told reporters last month that Manafort worked for him "for a very short period of time".
If there's an acquittal, however, that likely hurts the Mueller probe in the court of public opinion, fuelling calls for his investigation to wrap up and, in an extreme scenario, emboldening Trump to fire the special counsel.
What's likely to be missing: answers about whether the Trump campaign coordinated with the Kremlin during the 2016 presidential election, or really any mention of Russian Federation at all. And there's always the possibility that Manafort could take a plea deal during the trial if his defense falls apart, opting for a lighter sentence in exchange of telling Mueller's team anything he may know about possible collusion between the Trump campaign and Russian Federation.
One potential witness was even told to be cautious when speaking of Manafort's NY residence - he owns a condominium in Trump Tower in midtown Manhattan, sources told ABC News. The exhibits also "contain evidence about the identity of Manafort's sources of income in Ukraine, and in particular the oligarchs who instituted the practice of paying Manafort via foreign accounts", according to the filing.
"We have once again reached the point in time where we should cast aside all USA political work in favor of everyone's most beloved country - Ukraine", Gates wrote in a 2014 email to some American political strategists.
Gates pleaded guilty in February to charges of conspiring against the US and of making false statements to the federal government.
He's been in jail since last month when the judge presiding over the Washington case revoked his bail for allegedly tampering with potential witnesses.
The decision to drop the appeal comes one day before Manafort's criminal trial is scheduled to begin in Virginia federal court.