Not really. When you pay for .us domain you have it for a certain number of years. If the US tried to suddenly yank those back and violate the outstanding contracts for x number of years, there would most likely be lawsuits and an injunction from a federal judge blocking the action until there are hearings, etc. It would be a whole thing. If you simply couldn't renew your .us domain anymore, that's something you would know ahead of time and could plan for. It wouldn't just vanish one day.