(CNN) Prosecutors in the Paul Manafort trial are evoking a world of swaggering fraud, concealed millions and personal betrayal that allegedly festered in the lives of two big-time political operatives at President Donald Trump's side for crucial moments of his 2016 general election campaign.

In potentially the key moment of Manafort's tax and bank fraud trial, special counsel Robert Mueller's star witness, Rick Gates, took the stand Monday for 78 minutes of blockbuster testimony.

He lifted the lid on what is claimed to be a web of financial crimes that mocked taxpayers and bankrolled Manafort's life of opulence -- featuring gilded mansions and an ostrich skin jacket. Manafort has denied all the allegations against him.

Gates -- who has agreed to a plea deal in the hope of a reduced sentence -- dramatically turned on his former business partner, who he said possessed one of the most "brilliant" political minds he had ever encountered.

His appearance set up the core question of the trial: whether jurors will believe Gates' version of events or the defense case that Manafort was an innocent party who was deceived by his former protégé.

"Now the battle is between the admitted liar and the accused liar, and who are you going to believe?" Laura Coates, a CNN legal analyst, said on "The Lead with Jake Tapper."

Led by Mueller's prosecutors, Gates sketched out a network allegedly used to funnel millions of dollars from the pockets of Ukrainian oligarchs through the opaque banking system in Cyprus.

Perhaps most sensationally, Gates said that while he was helping Manafort set up their financial spigot, he was fleecing the longtime GOP operative himself -- turning in fake expense claims worth hundreds of thousands of dollars. A case of the alleged con man being conned.

The tale Gates wove will do nothing to dispel the impression that he and Manafort are the epitome of the Washington swamp, which Trump -- who they served as campaign chairman and deputy campaign manager -- ironically, pledged to drain.

Monday's drama would be a stunning Beltway story in itself.

But the fact that Manafort and Gates were members of the President's political brain trust -- who got a shoutout from Trump at a campaign event in July 2016 -- made it even more surreal and compelling.

Though the trial does not get into claims of collusion between the President's 2016 campaign and Moscow, it is implicitly establishing a nexus for the record between key figures in Trump's orbit and oligarchs believed to have ties with Russian intelligence.

And it thickens the intrigue surrounding the wider Mueller probe amid signs the special counsel is closing in on an increasingly nervous President, who CNN reported during the weekend worries that the investigation increasingly has his son, Donald Trump Jr., in its sights.

But the fracture between Manafort and Gates is also a human story -- of erstwhile partners enriched by allegedly illegal schemes but now split by a gulf wider than the courtroom in which they sat separated by a few feet and where their relationship splintered into smithereens.

Manafort, the former Trump campaign chairman, who spends his time away from court in jail, fixed Gates with a death stare as he took the stand.

Gates did not return his former partner's glare.

In his eye-popping appearance, Gates said he had helped Manafort commit crimes, that they had opened 15 foreign accounts they did not report to the federal government and knew were illegal, and that he had lied on behalf of his former boss.

Gates, who has a young family and faced the prospect of a prolonged jail term had he not signed the plea deal, said bank accounts in Cyprus they used when helping a politician on the island were used to funnel millions of dollars from the oligarch backers of their political clients in Ukraine.

As he left the courtroom and headed to the elevators, Gates was seen holding a Dan Brown thriller.

He probably needs some escapism given his grim predicament. But he created some unique plot twists of his own in the long-awaited showdown. And he's back on the stand for more Tuesday morning.