When is he going to jail, though? Going to be difficult to run for office from a cell. Doesn't sound like a sensible investment from the Winklevii. Or it's just a ridiculously expensive political statement.
I don't know that anyone believes that the former US president will end up in prison, especially since he is a presidential candidate, which complicates the situation significantly. I think that there is a certain number of people in high politics who want to see him in prison, but I also think that there is a very large number of influential politicians and businessmen who are doing everything they can to prevent this from happening. The twins are just one more in a row playing a card that seems to be winning for them at the moment - and even if Trump doesn't win, those 15 BTC is not something that means too much to them.