Trump is simply insanely obsessed with what happened in the last election. But now he is president, and the fact that he may not have colluded with the Russians doesn’t mean he does not, as president, have a responsibility to ensure that the Russians be punished for interfering in our last election on their own and be effectively deterred from doing so in the future. That is in his job description.

Listening to Trump, it was as if Franklin Roosevelt had announced after Pearl Harbor: “Hey, both sides are to blame. Our battleships in Hawaii were a little provocative to Japan — and, by the way, I had nothing to do with the causes for their attack. So cool it.”

There is only one message Trump should have sent Putin in this meeting today: “You have attacked our democracy, as well as two core pillars of the global economic and security order that have kept the peace and promoted prosperity since World War II — the European Union and NATO. We are not interested in any of your poker-faced denials. Just know that if you keep doing it, we will consider it an act of war and we will not only sanction you like never before, but you’ll taste every cyberweapon we have in our arsenal — and some of your most intimate personal secrets will appear on the front pages of every newspaper in the world. Is there any part of that sentence you do not understand?

“So we will be watching you between now and our midterm elections,” Trump should have added. “I’m sure you know the date. If you behave well, we’ll talk again in December 2018 about anything you want — Ukraine, Syria, Crimea or arms control. Until then our C.I.A. and N.S.A. are on to you and your cyberspooks. And Vlad, as you may have noticed from my Justice Department’s recent indictment of 12 of your agents, you are not as good as you think.”

That is what a real American president, sworn to protect and defend the Constitution, would have said to Putin today. He would have understood that this meeting had only one agenda item — and it was not developing an “extraordinary” relationship.

It was d-e-t-e-r-r-e-n-c-e — deterrence of a Russia that has been increasingly reckless and destabilizing.