If there asset is in there position and no one can take it from them then yes they could able to do it especially if all legislators would agree on what their President want to happen.

Also they already made that decision and so far US is doing good for holding lots of Bitcoin coming from those seize assets they get from somewhere else.

But look at this they are also open on possibilities buying Bitcoin https://cointelegraph.com/news/us-treasury-still-exploring-budget-neutral-bitcoin-buys-secretary-says so for sure that they won't stop doing those things they currently done like relying on seize assets since for sure they are thinking about buying to increase their Bitcoin volume, remember they always want to be on top.