We have no choice. The unfolding calamity in Ukraine demands that we all set aside our usual pet debates — climate change, COVID, January 6, etc. — and try to get our heads around what we’re watching and what it means.

The magnitude of this horror show is now settling in. Ukraine’s dogged defense has been truly inspirational, but if the Russian war machine keeps grinding ahead and into NATO territory, that could lead to continent-wide conflict — or, infinitely worse, to nuclear war. History books (if they exist) might look back at today as the day the wheels came off.

That sounds macabre, I know, but we’ve not been this close to the brink for decades.

Optimists among us may be inclined to consider Ukraine as a far-away problem. It’s not. That’s a mistake we made after World War I when America reverted to being an isolationist nation hiding behind our two big oceans. That worked until Pearl Harbor, and the collapse of Europe taught us that we were not buffered from unwanted hostilities after all; we were squarely in the center of a world at war. So much for wishful thinking.

Like it or not, our world is much smaller and more inter-connected than it was in 1940. We can weather higher gas prices and other economic disruption, but what if Russia keeps going? Think cyber warfare or nuclear warfare — two horrendous outcomes that could take the world to its knees in a heartbeat.

Considering the wide range of possible directions that Russian and Chinese aggression might take, I believe that top U.S. priorities going forward are threefold: project strength, not timidity; move urgently to regain energy self-sufficiency; and, above all, steer clear of nuclear war.

The latter is the X-factor. Vladimir Putin’s assault on Ukraine is not going well, and he knows it. If nothing else, the events of past weeks have shown that he is not at all troubled by the human carnage he’s causing. Is it beyond the realm of possibility that in his frustration he could choose to eradicate Kyiv with a tactical nuclear weapon? And if so, where does that stop?

Anxiety about nuclear war may seem like a crazy notion, but it’s the crazy notion we’ve willfully put out of our minds for far too long. Putin’s announcement this past weekend that he is activating Russia’s nuclear alert status was a provocative escalation — perhaps just posturing, but far too serious to ignore.

I believe that the one truly existential crisis facing our planet — and everyone in it — is the presence of thousands of nuclear warheads, many far more powerful than the bombs that decimated Hiroshima and Nagasaki in 1945, weapons that are now in the hands of despots (Putin, for example) reckless enough to actually use them.

In light of that possibility, however remote, the central questions facing the U.S. is when and how we should engage more forcefully to preempt further escalation by Russia. Too soon could be perilous; too late could be catastrophic.

Our challenge, of course, is finding a way to block Russia’s advance without igniting the nuclear conflagration we’re intent on avoiding. Our actions should be measured and sharply proscribed. They could take many forms, such as interdicting Russian supply lines, providing American air cover, or derailing the country’s oil and gas business. Most importantly, we must make it clear to Putin that everything is on the table.

I believe our decision on next steps should be driven by the enormous and proximate risk posed by Putin’s aggression — and not unduly constrained by our prior self-imposed limitations or by NATO unwillingness to act. Our role as a NATO member gives us a valid excuse for not taking military action in Ukraine, but it does not prohibit us from doing so.

Further, despite the likelihood that China will pounce on Taiwan if we become entangled in Ukraine, I believe our first and highest objective must be to cut the head off the Russian snake in Eastern Europe. And doing so may prompt second thoughts in China about American resilience in the face of lawless aggression.

As a practical matter, Putin could probably unleash tactical nuclear weapons much faster than we or NATO could stop him; but therein lies the urgency of ratcheting up the pressure immediately. We simply do not have time to wait and see what he’ll do next. Confronting him now might be premature — but it also might save the world.

As Apollo 13 astronaut Jack Swigert famously said: “Houston, we have a problem.” We surely do, and at the moment, everything else can wait.