You have no understanding of what “international law” is. International law is created when two nations sign a treaty. They then treat the terms of the treaty as their respective national laws. Russia certainly had no problem violating international law when it decided to violate the Treaty on Conventional Armed Forces in Europe in 2007. Incidentally, Putin did that by issuing a decree. It was not done by a vote in the Duma.
The U.S. has the same right to cease complying with treaties it has signed.
In this case, as Russia didn’t sign ANY treaty with the US either concerning Ukraine or Crimea, so they can do as they please. And the US have not a word to say about it.