It wont matter, they can drop what ever they want, sanctions will screw them.
I am not so sure. Let's see:
1. Russia - main export goods natgas, oil, palladium and so on - all things with intrinsic value. Harder to sell under US sanctions, but the market is there. Can be happily sold for other currencies or BTC.
2. USA - main export good is USD. No intrinsic value. Only accepted because other countries view it as THE currency. Can be replaced by any other form of numbers in computers.
Who is more vulnerable ... (both have nukes)?
I think we in the UK are in the same Boat as the USA.
UK - Main export? fuck knows. Office worker types no doubt.