Any nation can sanction the US. Doing so would hurt its economy rather than America's, but they are certainly capable of doing it. All nations have the right to regulate trade, which means that the US has the right to impose sanctions. The US can and should use sanctions to stop Iran from getting nuclear weapons.
Yes, the real question is... Why would the US want to impose economic sanctions on a country? For peace? Their arsenal of weapons is quite impressive and they can intimidate many countries..I think this is a more subtle cloak and dagger method intended to get around most peoples thought processes.