We will update this post as further details emerge....
UPDATE: "Some people say" (ahem) that this article in Politico was the straw that finally forced Manafort out. It details that Manafort worked for a political party in Ukraine called "Opposition Bloc, which won some seats in Parliament during an October 2014 election."
Manafort's Ukraine business partner and protoge Konstantin Kilimnik (KK) operated the firm locally.
At some point, Opposition Bloc had stopped paying what it had owed Manafort’s firm, according to people familiar with the situation. They said that the party still owes Manafort’s company a significant amount of money.
When the party stopped paying its bills, Manafort’s Kiev office, which was being run by Kilimnik, began running late on its rent and employees’ salaries, according to several people familiar with the situation.
Not paying people. That's a familiar Trump refrain!
Another former team member said “KK is averse to conflict, so when the money wasn’t coming in, he just went dark and that pissed a lot of people off.” The former team member recalled that when Manafort traveled to Kiev in 2015 to try to secure the cash he was owed, he was “ambushed” in the lobby of the city’s Hyatt hotel by the landlord for his office demanding back rent.
There's also the words "private-equity fund in the Cayman Islands" are the least weird words in this Politico article.
UPDATE 2: Josh Marshall says Manafort is looking at jail.
I suspect it will simply be too clear cut, too out in the open for everyone to see for the DOJ to ignore. That alone is a serious violation of criminal law that can lead to up to five years in prison. Just as importantly, once that kind of investigation gets started a lot of other things that were never supposed to see the light of day or be exposed to investigative scrutiny suddenly get a hard look. How far that goes, well it connects to other high profile people is for now a matter of speculation. On the FARA [Foreign Agent Registration Act] compliance front itself, there's not much to speculate about. He's got a real problem on his hands.
The thing is, Manafort's violations were easily fixed if he just filed, but Trump either was too incompetent to notice or too corrupt to care. Either way it's another reason he shouldn't be President of my PTA, let alone the country.