WWIII has already started in Ukraine. Europe and the U.S. should wake up. | Trudy Rubin

“This war is for all the world,” a haggard Volodymyr Zelensky told CNN from an underground bunker, surrounded by sandbags. The incredibly brave Ukrainian president is correct.

Ukrainians are fighting for us, for the United States, for Europe, for you, for me. To say, as Zelensky did, that his countrymen are fighting for “democracy and freedom” is absolutely right but may be too abstract for many Americans to grasp.

Let me put it in more concrete terms:

If Russia’s Vladimir Putin can take over a peaceful country by brute force in the 21st century, and deliberately slaughter civilians to achieve his goals, then we are all at risk. He will not stop with Ukraine.

If Putin can openly threaten nuclear war to scare off NATO from halting his aggression, then much of Europe is in danger. If this deranged killer can play dangerous games with cyberattacks and nuclear weapons, then the threat extends across the Atlantic to the United States.

» READ MORE: Putin must be stopped from turning Kyiv into Aleppo | Trudy Rubin

“The Third World War has already started,” former Ukrainian Deputy Prime Minister Ivanna Klympush-Tsintsadze, told me via a WhatsApp call this week. Only three weeks ago, I was meeting with her in her office at the Ukrainian parliament, whose members are now on Putin’s hit list. The Russian war criminal has already sent vicious Chechen hit teams into Ukraine to assassinate its leaders.

“How many states must be destroyed before the West wakes up?” Klympush-Tsintsadze asked, her voice rising.

“The nuclear threat is here already. The Russians have already taken over Chernobyl [the site of the 1986 nuclear disaster]. Their fighter jets are hanging over Chernobyl as they fire at our cities and we cannot fire back because they are in a nuclear zone.”

There are other, still active nuclear reactors in Ukraine, she said, that are also at risk.

As if to prove her point, on Thursday, Russia attacked and seized Ukraine’s largest power plant, causing a fire. Mercifully, the reckless attack did not cause a radiation leak — this time.

Klympush-Tsintsadze is convinced that the West still doesn’t understand the magnitude of the threat posed by Putin, who wants to redraw Europe’s boundaries by force and uses the methods of Adolf Hitler.

“I think the whole international community is still several important steps behind Putin,” she told me. “Serious sanctions should have been applied before the war. And even with all the new sanctions and promises of more weapons, they are arriving very slowly because they have to travel by road,” since major airports have been knocked out.

But what disturbs this political activist most deeply is that her country lacks air defenses. Yes, the United States and Europe are now delivering thousands more shoulder-fired Stinger antiaircraft missiles. However, Ukraine lacks a surface-to-air system that can defend against Russian missile bombardments meant to destroy cities and wipe out civilians.

“For us every minute means lives,” she said. “Right now we are begging for a no-fly zone.” This is a plea made repeatedly by Zelensky. It means that Western aircraft would patrol Ukrainian skies and prevent Russian planes from attack.

That, however, would mean direct confrontation with Russia, which the United States and NATO understandably want to avoid at this moment.

Yet, as Russia proceeds in its efforts to hurt Ukraine so badly that its government will resign, President Biden and the European allies are going to have to think unthinkable thoughts. They must strategize about how to deter a leader who thinks his nukes make him impervious to Western pushback against his aggression.

“How many drastic miscalculations has the West made underestimating Putin and trying not to provoke him?” Klympush-Tsintsadze demanded.

This is a question President Biden and European leaders must confront not tomorrow, but today.

That’s because this ugly, unprovoked war is only going to get grimmer, as Putin tries — literally — to destroy the Ukrainian army and government by pulverizing cities to make Ukraine surrender.

But Ukrainians won’t bend. I spoke with Oleksiy Goncharenko, a parliament member whom I also met in Kyiv a few weeks ago. He represents the people of the exquisitely beautiful Black Sea port of Odesa — which is next on Putin’s hit list, as Russian amphibious landing warships loom offshore. “Nobody knows how long we can hold out,” he told me this week. “We are fighting hard, but our resources are incomparable with Russia’s.” Goncharenko has signed up with a volunteer defense unit and has been patrolling the streets.

He urges the West to sanction Russia’s oil and gas sales, which hasn’t been done yet — and, of course, also asks for a no-fly zone.

The courage of Ukrainian leaders and ordinary citizens presents Biden and our European allies with an urgent dilemma that has not yet been fully faced.

The belated surge of defense weapons to Ukraine may be too little, and too late to prevent Putin from laying waste to much of the country. These war crimes will be committed in full view of the world. And the Ukrainians will keep resisting their would-be conquerors, no matter how many cities fall.

Biden must prepare Americans, more than he has, for a long-running conflict that will inevitably hurt Americans economically as gas supplies and international trade are disrupted. And he must explain why this is America’s battle, too.

Furthermore, he and European leaders must contemplate out-of-the-box methods to fight back against Putin, within Ukraine, and to protect other non-NATO countries. (Biden’s warnings to Moscow about not touching NATO member countries was on point, but must be more strongly reinforced.)

Oil and gas sanctions, air and missile defense systems, covert activities, even a no-fly zone over western Ukraine must all be strongly considered to stop this war criminal — and to prevent him from inspiring other dictators from following his lead.

» READ MORE: Ukrainians are ready to fight against the new Hitler. His name is Putin | Trudy Rubin

And — crucially — GOP leaders must finally chastise those in its ranks, including Donald Trump and Fox News’ Tucker Carlson, who praised Putin after this war began. They are enabling a war criminal, who feeds off the U.S. political divisions they sow.

Western efforts will be aided by the ongoing sacrifices of Ukrainians, who won’t give up fighting the Russians no matter how many cities fall.

One of my most emotional WhatsApp talks this week was with my Kyiv translator Lena Stepanova, who has moved to her mother-in-law’s small town two hours outside Kyiv. Though the town has not yet been attacked, almost every citizen is working on the war effort. Lena has joined many women in tearing up fishing nets and fashioning them into camouflage nets for tanks.

Others are making Molotov cocktails by pouring gasoline into beer bottles with wicks made from rags. Or using metal wires to make antitank weapons that can be strewn on the roads.

“We have so many volunteers, we don’t have work for all of them,” she said. Schoolchildren are running around looking to wipe out fluorescent markers apparently left by local Russian spies to mark possible bomb targets. There are more men than there are guns, so local territorial defense forces are trying to seek out the spies.

Will she keep fighting back even if the Russians arrive? “Of course,” Stepanova said. “This is our country. We have no choice.”

And Americans have no choice but to help the Ukrainian resistance — to deter Putin from further threatening the world.