Once federal investigators cut into you, and if they have the motivation (like you not cooperating) they will tear into you, and anything around you like rabid dogs. That is just what they do. The mitigating factor is money...if you have long money, fukk you money, you can fight the feds, but it is draining, and esp. if you are accused of financial crimes, they start cutting you off from all your assets.
The case recently that underscored this, was the Japanese/Mexican businessman, in San Diego, reputed a billionaire, but not really, who was indicted for illegal campaign contributions, he hired a team of lawyers, and fought it to the very last. They indicted him, and his son, and retried him on a firearms charge they deadlocked on. He was convicted of 36 counts, and in the end, only sentenced to 3 years in prison, and a 500,000 fine. So, he kind of prevailed there, but he must have paid a few million over the last 4 years to fight the case.
Manafort is trying to fight, but they are stacking the deck, AND cutting off his cash flow, and his co conspirators are talking.