It's not just that Paul Manafort is accused of laundering tens of millions of dollars in Ukrainian payments, it's that he's accused of working with U.S. adversaries to earn that money.
For a start, consider that the Department of Justice indictment accuses Manafort of working for the "Party of Regions" up until its implosion following the 2014 "Maidan" revolution. More importantly, under the 2010-2014 premiership of Viktor Yanukovych, the party was firmly in the pocket of Russian President Vladimir Putin.
The most notable success for Putin here was Yanukovych's acceptance of the 2010 Kharkiv Pact, in which Russia acquired long-term rights to retain a naval base in Crimea. While Crimea is obviously now under Russian control, the situation in 2010 was far from affirmed and Yanukovych's decision reflected the obvious power of Russia's influence. While in power, the party also distanced Ukraine from a closer-cooperative relationship with the United States and the European Union, while doing nothing to clamp down on organized crime.
But if the "Party of Regions" was bad, the "Opposition Bloc" formation that followed the 2014 revolution is even worse.
After all, that political grouping is a formalized relationship between the mafia and politics. Supported by oligarch-crime lords such as Yuri Boyko and Rinat Akhmetov, who made their money securing lucrative contracts in the post-Soviet era, the bloc finds its political support in pro-Russian areas of eastern Ukraine. Yet holding significant assets in the U.K., many of which have been registered through shell companies in tax-regulatory havens in the Virgin Islands, Opposition Bloc leaders have been able to match their political advocacy with luxurious lives in the west.
Indeed, they have also successfully presented their case in U.S. media. One Opposition Bloc official, Sergei Lyovochkin, has written articles for Time, Politico, and the Wall Street Journal. The sustaining message is focused on a pro-Russian agenda of greater decentralization in eastern Ukraine, weakening the Ukrainian government's military response to the Russian-supported insurgency, and diluting the influence of the pro-American ruling government in Kiev.
Still, as it pertains to Manafort, the simple takeaway here is one of money: in order to maximize their slice of the pie and retention of lucrative economic interests, the Opposition Bloc is willing to pay big dollars to anyone who can help them. This is not to say that the ruling government does not have its issues with corruption (it does), but for those who oppose Russia in Ukraine, the risks are far higher.