According to a SWISS representative on Twitter, you need to specify the destination country, which in this particular case is the US:
Yes, then it would be the country you’re travelling to.
https://twitter.com/FlySWISS/status/1087295723387932672
I’m personally not very happy with the lack of common sense in the way the check-in form is composed, but that is the official answer. I can only guess that for some other destinations it is not as obvious whether or not a visa for one country would also allow entry to some other country due to some international agreements.
Upd: I followed the given advice and had no issues with the flight, expect for catching a cold on my way there because climate control in Swiss’s airplanes is apparently not a thing, even in cold Russian winters.
Credit:stackoverflow.com‘