You take a monthly total of hotel room payments from Russian guests across dozens of properties (rooms are $500/night and up at most Trump hotels) and add in charges for guest activities (booze, massages, etc.) and you're going to get some impressive numbers.
Go to a judge and say "look, in August we see payments of 12 million dollars from Bank of Moscow going to a Trump server" and you have something that sounds impressive.
Yes, there is something very Watergate here. Especially when seen in the context of the "rigged" Hillary Clinton nomination process.