President Obama on Friday called on Russia to withdraw its troops from the border with Ukraine, saying Moscow's behavior "is not how international law and international norms are observed in the 21st century."

“Well, on this I think he’s been willing to show a deeply held grievance about what he considers to be the loss of the Soviet Union,” Obama told CBS News in an interview. "You would have thought that after a couple of decades that there'd be an awareness on the part of any Russian leader that the path forward is not to revert back to the kinds of practices that were so prevalent during the Cold War, but in fact to move forward with further integration with the world economy and to be a responsible international citizen. ...

“What I have repeatedly said is that he may be entirely misreading the West. He is certainly misreading U.S. foreign policy. We have no interest in encircling Russia and we have no interest in Ukraine beyond letting the Ukrainian people make their own decisions about their own lives.”

Why does affect what the U.S. response should be? The answer: It doesn't.

What Obama continues not to understand is Russia's motivations are irrelevant to what the U.S. needs to do to protect its own interests when confronted with the fact of Russian aggression against Ukraine -- aggression that violates written assurances given by Russia to the U.S. in the 1994 Budapest Memorandum.

As I've said before, what matters most is Russia's betrayal of its word to the United States -- not Obama's legalistic arguments, which, in any case, have had no discernable impact on Moscow, nor his pinprick sanctions that Russian officials have laughed off.

That betrayal makes a mockery of one of the most significant victories for nuclear disarmament in the past 20 years: the scrapping of what was at the time the world's third-largest nuclear arsenal. Unless addressed, it sends a signal to the world that there's no benefit in giving up ambitions to become a nuclear power (and you can bet Iran is watching). It also clearly states that Obama -- when push comes to shove -- will not act to protect what he says is one of his highest foreign policy priorities: progress toward nuclear disarmament.

It's time for Obama to stop psychoanalyzing Russian President Vladimir Putin and arguing legal technicalities. The world needs to know what the United States will do to enforce its agreements.