America is currently the most powerful country in the world by far, I don't think anyone will disagree with that.
But they have chosen not to fight against Russia, whether in Georgia or Ukraine.
And the sanctions are just lip-service, no one in the West will boycott Russia.
2008 can be thought of as when US lost its newly found "hyper power" status after the fall of Soviet Union.
Russia recovered enough after the fall of Soviet Union by then and it made a statement that it has the power in its backyard.
Anyway US knows that getting into war with Russia and China could mean death for them and so will only do so as a last resort.
US respects no nations apart from Russia and China.