This has been the presumption for some time, of course. Robert Mueller wasn’t appointed to prosecute bank fraud cases. He was appointed to find out if the Trump campaign colluded with Russia. So why is he prosecuting Paul Manafort on an unrelated bank fraud case?
The answer is obvious: He’s doing it for the same reason he had his team stage a 6 a.m. raid of Manafort’s home at a time when Manafort was already cooperating with him. He’s trying to harass and intimidate Manafort into flipping and giving Mueller something he can use to bring down Trump.