President Volodymyr Zelensky of Ukraine called on Joe Biden to be “the leader of the world” when he spoke before Congress Wednesday, but it’s clear that for the moment, Zelensky is the leader of the world — at least when it comes to providing us with a sterling example of what leadership can and should be.

Stalwart. Responsive to emotion but not driven by it. And with a determined sense of what is right and what is wrong, and what is necessary and unnecessary.

“Strong doesn’t mean brave or big,” he said, which is a sentence worth studying. He wants it to be understood that Ukraine should not be supported because it’s bravely taking a stand against a superior power it is not likely to prevail against.

No, Zelensky was saying, support for Ukraine is not a sentimental or foolhardy gesture, because Ukraine is “strong.” It can win this. It can do so if we give Ukraine the tools that will help it “close the sky.” We won’t just be doing our humanitarian duty in preventing the kinds of horrors he showed us during a heartbreaking film clip cataloging the cost of Russia’s depredations.

His relatively brief, substantively fascinating, and ultimately overwhelming speech will not only strengthen the determination of the American people and the West to support Ukraine but will deepen that support. For example, he moved beyond the plea for a “no-fly zone” that Biden thinks is too provocative. “Is this too much to ask?” Zelensky said, then answered: “If this is too much to ask, we offer an alternative.”

The alternative was, specifically, a Soviet-Russian air defense system called the S-300 that would have to be transferred to Ukraine by a NATO country formerly in the Soviet bloc where it had once been deployed. Our role would then be to replace that system in Poland (or wherever else) with a newer American system.

Get the latest updates in the Russia-Ukraine conflict with The Post’s live coverage.

Cannily, he did not push on a closed and possibly locked door, but rather opened a side door to a new kind of resistance capacity against the Russian onslaught. That shows Zelensky’s capacity to improvise and think creatively about how to continue the fight he and a growing number of Western war experts think might actually be winnable.

The speech (and his film) will also put salutary pressure on America’s elites — not just in the Biden administration but in Congress and the chattering classes — not to start “going wobbly.”

That was what Margaret Thatcher told George H.W. Bush to buck him up the last time the nations of the West gathered to oppose and seek to reverse one country’s gobbling up another — back in 1990, when Saddam Hussein’s Iraq took over Kuwait.

Right now, the emotional direction of the country is all toward Ukraine, but despite the general idea that the US public is fickle and will lose interest or focus, the graver threat to Ukraine comes from the elites and their collective lack of a policy spine. That temptation — to think that there might be a way to squirm out of taking a stand — is what Thatcher was warning the elder Bush against 32 years ago.

And it’s a good reminder now that if the Ukrainian people are willing to suffer these awful consequences to remain free of the Russian yoke, we can at least stand shoulder to shoulder with them and give them the support we can.

Zelensky, a comic actor by trade who seems to have answered history’s unexpected call in the most extraordinary fashion, is the face of Ukraine, and the representative of its heart and spirit. He is the bracing antidote to the terrified defeatism and existential fear that seem to have overcome this country during the pandemic years.