People seem to want the USA to become judge and jury here and excise some pound of flesh from Russia. The problem is that the US's only standing, short of military actions, is that of mediator. And it would be absolutely INSANE to start threatening Russia with military action over this.
Thus, it is neither the US's place, nor ability to seek whatever form of "justice" people in this thread are demanding.
The option here is diplomacy. The US can stand in as a mediator to help broker a deal. To even be able to take that role, Trump can't just start insulting Putin, blaming Russia, and promising to get for Ukraine at the expense of Russia. He has to either walk as a diplomat, or pull out US interest altogether and let them hammer it out, at the expense of more lives every day.
It is so funny. We were assured that Trump could never be the Presidential diplomat because he was supposedly too volatile to work for a big picture, yet his detractors prove to be exactly what they accused him of, and he's just the opposite.