That fact could compel someone previously or now close to the president who knows of any illegal activity to come clean or act as a co-operating witness if they have information relevant to Mueller's Russian Federation probe.
As a result of their work with Ukraine, Manafort and Gates made tens of millions of dollars between 2006 and 2015.
Manafort has pleaded not guilty to all the charges.
On Monday, prosecutors said in court filings that they meant to prove Manafort earned more than $60 million lobbying for the former pro-Russia Ukrainian government and failed to report "a significant percentage" of that.
The luxurious lifestyle was funded by Manafort's political consulting for the pro-Russian Ukrainian political party of Viktor Yanukovych, who was deposed as Ukraine's president in 2014.
In pretrial arguments, prosecutor Greg Andres told the court the government would only bring up Manafort's campaign work in the context of a witness from a bank who gave him a loan, with the expectation that the banker would win consideration for a post in the Trump administration. But when the special counsel hit the two men with a second indictment in February, Gates pleaded guilty to two lesser counts in exchange for cooperation.
Joshua Dressler, a law professor at Ohio State University, said the evidence against Manafort, 69, appeared strong but that he drew a favourable judge in the 78-year old T.S. Ellis, who is known to be tough on prosecutors.
Manafort has been charged with four counts of bank fraud and five counts of conspiracy to commit bank fraud. However, Ellis denied Manafort's request to dismiss the criminal charges against him, saying his lobbying work "warranted the investigation here".
Manafort was no stranger to politics, having also served as an adviser on the campaigns of President Ford, President Reagan, President H.W. Bush, and Bob Dole.
The judge told potential jurors the trial would last no more than three weeks.
About 500 pieces of evidence have been submitted by investigators, including luxury watches and pictures of lavish homes, and up to 35 witnesses could be called.
Lawyers working for special counsel Robert Mueller plan to call witnesses they say demonstrate where Manafort spent his allegedly ill-gotten gains: custom-made suits; Persian rugs; landscaping fees; Land Rovers and Mercedes-Benz vehicles; and season tickets to the New York Yankees, among other items. He was originally hired to secure votes from delegates at the Republican National Convention but was promoted to campaign chairman after Mr. Trump fired Corey Lewandowski in June.
Mueller's team said it would not present evidence at the trial in the Washington suburb of Alexandria, Virginia, about possible campaign collusion with Russian Federation, potentially saving it for a second Manafort trial in Washington in September. Mueller's original mandate was to investigate not only potential collusion between the Trump campaign and Russian Federation, but also any other crimes arising from the probe. "Didn't know Manafort was the head of the Mob".
The trial will afford the public its first glimpse of a defence that so far has focused less on the substance of the allegations than on Mueller's authority to bring the case in the first place.
Manafort has withdrawn his appeal of a judge's decision to throw out his civil lawsuit against Mueller, according to court filings.