There are indeed many forms of money laundering which are considered illegal in America, and it is absolutely illegal if someone is accepting funds derived from illicit activity or sanctioned entities (like Russia). The government and most financial institutions generally take the stance that there are very few good reasons to obscure the ultimate source of funds, and so tend to be very risk-averse with such activity.
The trick is in confirming anything illicit is going on when there are potentially dozens of steps and borders in between the source and the recipient.