Well, If the US do bid, the candidate would probably be Anchorage or Salt Lake City or even Denver (Bit hard since they withdrew in 1976), it would be hard for them if they get 2024, Asia can be ruled out straight away, we've seen too many games from them so goodbye Sapporo (Not saying the bid is going to be rubbish or poor, just saying it'll be hard for them too) South America would probably have Santiago (It would be a favourite, but I think they would use this as a test bid for the future?) Leaving Europe, The only strong bids from Europe that I can think of would probably be:
Barcelona, Spain
The Joint Bid from Norway and Sweden
and Sion
I'd say the toughest cookie Sion would have to get past is Barcelona...