The difference is that in the case of the US that was a lie. And Ukraine being a US proxy is not actually the weaker party in this, Russia is because they don't have the full backing of an alliance like NATO behind them. So Russia was entirely justified in feeling threatened by a militarized russophobic Nazi regime, not on the other side of an ocean but right on their border, wanting to join a hostile military alliance who openly declare that their principal enemy is Russia.
People who try to draw superficial comparisons between Ukraine and Iraq are lying by omission because literally everything about this is different.